help needed with Nav!!
Tinstaafl - you have just demonstrated what a total crock of $hit the 1:60 rule is for simple PPL VFR navigation. Something which most of the world accepted over 30 years ago.
The only trouble with the SCA method is that ageing dinosaurs can't believe that navigation can be so simple!
bookworm - now read my earlier post more carefully. After getting back on palnned track, apply only the observed drift error. No need to do both at the same time.
The 'not invented here' syndrome infests many of the gold bars on pullovers schools...
The only trouble with the SCA method is that ageing dinosaurs can't believe that navigation can be so simple!
bookworm - now read my earlier post more carefully. After getting back on palnned track, apply only the observed drift error. No need to do both at the same time.
The 'not invented here' syndrome infests many of the gold bars on pullovers schools...
BEagle
Whether you apply SCA and drift error or just SCA, the number of numbers to be dealt with remain the same.
FWIW, your geometry only works if you apply the drift error while getting back on track. It matters less only because the correction is so coarse for larger SCAs that continuing to drift happens for such a short time. If you envisage a 360 kt scenario with a 10 degree SCA and a 10 degree drift angle, applying only the SCA will simply parallel the desired track.
Whether you apply SCA and drift error or just SCA, the number of numbers to be dealt with remain the same.
FWIW, your geometry only works if you apply the drift error while getting back on track. It matters less only because the correction is so coarse for larger SCAs that continuing to drift happens for such a short time. If you envisage a 360 kt scenario with a 10 degree SCA and a 10 degree drift angle, applying only the SCA will simply parallel the desired track.
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BEagle,
Having put nice 6 minute time marks on your chart, and having discovered in flight that the met officer gave you the wrong wind would you not agree that the marks you made are useless clutter for the average PA28 pilot since they were made with the wrong wind?
Personally I favour fixed positions based on recognisable features. You can mark your map once and use it on a thousand flights with different winds. It is also how airways are navigated using reporting points.
The RAF like SCA because in a fast jet it works well as you said. They also favour fixed time marks because they are very interested in achieving a TOT and they have the ability to increase or reduce speed as necessary to stay on time.
Instructors who use SCA or double the error agree on one thing, getting back onto the planned track is important. Thus both are in general achieving the important point of the exercise. As long as we don't have pilots 5nm off track correcting direct to destination then we overall agree.
I believe that correction should be made using the appropriate method within the first 15 minutes maximum.....about 10nm out in a PA28. That takes care of tracking. A Fix close to the quarter of halfway mark will sort out timing.
Remember that a PA28 pilot navigates far better than any fast jet pilot to achieve the same accuracy!
Regards,
DFC
Having put nice 6 minute time marks on your chart, and having discovered in flight that the met officer gave you the wrong wind would you not agree that the marks you made are useless clutter for the average PA28 pilot since they were made with the wrong wind?
Personally I favour fixed positions based on recognisable features. You can mark your map once and use it on a thousand flights with different winds. It is also how airways are navigated using reporting points.
The RAF like SCA because in a fast jet it works well as you said. They also favour fixed time marks because they are very interested in achieving a TOT and they have the ability to increase or reduce speed as necessary to stay on time.
Instructors who use SCA or double the error agree on one thing, getting back onto the planned track is important. Thus both are in general achieving the important point of the exercise. As long as we don't have pilots 5nm off track correcting direct to destination then we overall agree.
I believe that correction should be made using the appropriate method within the first 15 minutes maximum.....about 10nm out in a PA28. That takes care of tracking. A Fix close to the quarter of halfway mark will sort out timing.
Remember that a PA28 pilot navigates far better than any fast jet pilot to achieve the same accuracy!
Regards,
DFC
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why is track crawling so derided in lower level Day VFR flying? If my track line passes over or alongside prominent features why wouldnt I point the aircraft toward said feature, draw an imaginary line over the ground to the feature and follow it, as you approach it look for the next etc. etc.
You wouldnt need worry about poor or no available forecast, 1-in-60's, whizz wheels et al.
Of course, time checks and cross reference to compass and usual airmanship points apply.
Just a query.
You wouldnt need worry about poor or no available forecast, 1-in-60's, whizz wheels et al.
Of course, time checks and cross reference to compass and usual airmanship points apply.
Just a query.
Actually, I wrote:
Timing marks every 6 minutes may be added as must the exact elapsed time at readily identifiable visual fixes roughly corresponding to easy fractions of the way along the leg (to make proportional timing correction reasonably straightforward) and at the turning point.
which means put 6 minute marks on if you wish (I don't bother), but do put times against readily identifiable visual fixes. You don't need many of these (one about every 10-15 mins should suffice), but choose them at some simple fraction of the leg length - i.e. a nice obvious fix at 30% of the way along the route can be treated as 'about 1/3 way along track' for timing correction, whereas an exact point in the middle of nowhere at exactly 50% of the leg is pointless.
Also, for the terminally dim who still seem unable to read, once you've established where you are to make the 'miles off track' estimate, you turn back to track for the appropriate time. In the time you are chugging back towards track, double check the distance and jot down the timing correction. No need to add it up there and then, do that later. When you're back on track, then and only then check that the DI agrees with the compass, that the ball is centred and ask yourself whether your flying had been nice and accurate thus far. If the answer to any of those questions was 'no', don't bother changing your heading from the original once you're back on track - blame yourself. But if the answer was 'yes', then the wind must have been the culprit, so use your single drift line assessment to correct by the same amount. No silly reciprocal-of-the-fraction-flown-multiplied-by-the-drift-angle to do in your head - just a single figure to add or subtract. If it's more than 10 deg, the weather-guesser must have been telling porkies!
Why is track-crawling frowned upon? One reason is that you spend too long staring at the ground and not looking out around you for other aircraft!!
Timing marks every 6 minutes may be added as must the exact elapsed time at readily identifiable visual fixes roughly corresponding to easy fractions of the way along the leg (to make proportional timing correction reasonably straightforward) and at the turning point.
which means put 6 minute marks on if you wish (I don't bother), but do put times against readily identifiable visual fixes. You don't need many of these (one about every 10-15 mins should suffice), but choose them at some simple fraction of the leg length - i.e. a nice obvious fix at 30% of the way along the route can be treated as 'about 1/3 way along track' for timing correction, whereas an exact point in the middle of nowhere at exactly 50% of the leg is pointless.
Also, for the terminally dim who still seem unable to read, once you've established where you are to make the 'miles off track' estimate, you turn back to track for the appropriate time. In the time you are chugging back towards track, double check the distance and jot down the timing correction. No need to add it up there and then, do that later. When you're back on track, then and only then check that the DI agrees with the compass, that the ball is centred and ask yourself whether your flying had been nice and accurate thus far. If the answer to any of those questions was 'no', don't bother changing your heading from the original once you're back on track - blame yourself. But if the answer was 'yes', then the wind must have been the culprit, so use your single drift line assessment to correct by the same amount. No silly reciprocal-of-the-fraction-flown-multiplied-by-the-drift-angle to do in your head - just a single figure to add or subtract. If it's more than 10 deg, the weather-guesser must have been telling porkies!
Why is track-crawling frowned upon? One reason is that you spend too long staring at the ground and not looking out around you for other aircraft!!
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track crawling
chines fella
track crawling is not derided but it is not 'Navigation'. Forecast winds are just that, forecast. It is important for the pilot to discover the actual w/v at the chosen flight altitude. Track crawling dosn't allow you to do that and wouldn't work over the North Sea.
The w/v is found by maintaining a constant heading and speed for a given time, following which any errors may be assessed for GS and drift using a number of differing techniques. You now know the actual w/v. This method is repeated at intervals throughout the flight. The pilot is able to revise and apply a good heading (even without surface features always being available) and of course the intermediate and final ETAs.
track crawling is not derided but it is not 'Navigation'. Forecast winds are just that, forecast. It is important for the pilot to discover the actual w/v at the chosen flight altitude. Track crawling dosn't allow you to do that and wouldn't work over the North Sea.
The w/v is found by maintaining a constant heading and speed for a given time, following which any errors may be assessed for GS and drift using a number of differing techniques. You now know the actual w/v. This method is repeated at intervals throughout the flight. The pilot is able to revise and apply a good heading (even without surface features always being available) and of course the intermediate and final ETAs.
Thank you for your considered opinion, Beagle. Now that that you've enlightened us all perhaps you could deign to explain your reasoning to support your emotive outburst. 
1:60 works. It works well, it's simple & it's flexible. Other methods also work. All methods have some disadvantages although I think on balance the 1:60 has fewest.
As far as I can see your favoured method offers no additional benefit.
Indeed, it locks you into a single correction factor. Bad luck if you wish to achieve track elsewhere eg a particularly recognisable point in relatively featureless terrain (this can also be a deficit for proportional nav & double the TE corrections). It also means you have to memorise a range of apparently arbitrary SCAs for a variety of a/c. How's that different to memorising the numbers 1, 2, 3, 4 (and '+ a half'). I would argue that your method, whilst useful at times, lacks flexibility and is no simpler particularly if you fly range of a/c. Granted, if you fly a single type then it can be a 'good thing'.
I would also wonder at the accuracy of SCA when there's a large difference between TAS & GS - a common occurance in light a/c.
1:60 works. It works well, it's simple & it's flexible. Other methods also work. All methods have some disadvantages although I think on balance the 1:60 has fewest.
As far as I can see your favoured method offers no additional benefit.
Indeed, it locks you into a single correction factor. Bad luck if you wish to achieve track elsewhere eg a particularly recognisable point in relatively featureless terrain (this can also be a deficit for proportional nav & double the TE corrections). It also means you have to memorise a range of apparently arbitrary SCAs for a variety of a/c. How's that different to memorising the numbers 1, 2, 3, 4 (and '+ a half'). I would argue that your method, whilst useful at times, lacks flexibility and is no simpler particularly if you fly range of a/c. Granted, if you fly a single type then it can be a 'good thing'.
I would also wonder at the accuracy of SCA when there's a large difference between TAS & GS - a common occurance in light a/c.
Since one can only fly one ac at a time, hardly much need to 'memorise a wide range of SCAs'.....
Personally I find 'right 40 deg for 3 minutes and delay ETA by a minute' a lot easier than trying to work out (3x60/17) + (3x60/38) in my head.....
Even if SCA doesn't get you exactly back to track, you'll be close enought to recognise your position at the next visual fixpoint
Personally I find 'right 40 deg for 3 minutes and delay ETA by a minute' a lot easier than trying to work out (3x60/17) + (3x60/38) in my head.....
Even if SCA doesn't get you exactly back to track, you'll be close enought to recognise your position at the next visual fixpoint
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Some more fell on stony ground I fear.
Those that UNDERSTAND SCA - use it if you wish,
those that don't - don't
and those that have an open mind - check out all the options and choose for yourself.
You have disappeared in to the vortex of "my mind is made up and the rest of you are wrong"
Understanding is the key to knowing
Me - I'm a SCA kind-o-guy.
ENDEX
Not listening no more
La,la,la,la,
Those that UNDERSTAND SCA - use it if you wish,
those that don't - don't
and those that have an open mind - check out all the options and choose for yourself.
You have disappeared in to the vortex of "my mind is made up and the rest of you are wrong"
Understanding is the key to knowing
Me - I'm a SCA kind-o-guy.
ENDEX
Not listening no more
La,la,la,la,
Er....where did you get the ".../17" or ".../38" bit fro6m??? 
I've run 27 or 30 or 35 nm (ie near-as-dammit 30 nm) & find I'm 4 nm off track. That equates to 8 deg TE (ie x 2). If I double that I'll be back on track in the same time & distance. I'll also know how much to alter heading in order to maintain track once there. Do you really think that's difficult?
I'll repeat the table:
approx Dist run or to go..........multiply dist off x to get Tr. Error or Closing angle
60...........................1 eg 4 nm off then TE=4 deg
30...........................2 eg 3 nm off, TE = 6 deg
20...........................3 eg 3 nm off, CA= 9 deg
15...........................4 need I continue???
45...........................add half the dist off to itself. eg 6 nm off, TE=9 deg
If I need/want to regain track at a specific point (eg in the desert where fixes are few) or even parallel track without closing then I can do that too. How is that done using SCA?
ETIs require a groundspeed check anyway. Adding a minute IAW SCA doesn't seem to allow for altered GS for the remainder of the on track route. Have I missed something?
I've run 27 or 30 or 35 nm (ie near-as-dammit 30 nm) & find I'm 4 nm off track. That equates to 8 deg TE (ie x 2). If I double that I'll be back on track in the same time & distance. I'll also know how much to alter heading in order to maintain track once there. Do you really think that's difficult?
I'll repeat the table:
approx Dist run or to go..........multiply dist off x to get Tr. Error or Closing angle
60...........................1 eg 4 nm off then TE=4 deg
30...........................2 eg 3 nm off, TE = 6 deg
20...........................3 eg 3 nm off, CA= 9 deg
15...........................4 need I continue???
45...........................add half the dist off to itself. eg 6 nm off, TE=9 deg
If I need/want to regain track at a specific point (eg in the desert where fixes are few) or even parallel track without closing then I can do that too. How is that done using SCA?
ETIs require a groundspeed check anyway. Adding a minute IAW SCA doesn't seem to allow for altered GS for the remainder of the on track route. Have I missed something?
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Tinstaafl,
With SCA or doubble the error, there is absolutely no requirement to have a feature on track at the point where the planned track is regained.
Using the SCA, you will be back on track in the standard time. Using doubble the error, you will be back on track in equal time.
Using the 1 in 60 rule to correct direct to the next checkpoint requires you to not only spot the next checkpoint because if you don't you are lost, it also has the problem that you are now following a new unplanned track offset from the planned track. You are comprimising you safety altitude calculations and possibly separation from regulated or special use airspace.
Furthermore, since the correction you made could be for a leg of 100nm or more to destination, any further error on the new track must be assessed with regard to the new track and not against the one carefully drawn on your chart.....or perhaps you think that having calculated the errors using 1 in 60, we should use a ruler to draw in our new track and make new checkpoints?
Get back on planned track asap has to win out....so SCA or doubble error whichever.
Track crawling has it's merits in some situations. It can be very appropriate in certain situations for example keeping clear on controlled airspace. If there is a decent feature - use it. Be aware that if you use traditional navigation you could drift off track between checkpoints so you must make an allowance for that ( a buffer) when flying close to regulated or special use airspace. If there is a well defined line feature (handrail) then pre-planned track crawling along that feature can ensure safe operation.
Another example is following the coast on the seaward side as when doing so, one can disregard obstacles inland for safety altitude purposes since you will not hit them provided you don't fly inland.....can reduse enroute weather minima for the route.
However, it must be an obvious feature and pre-planned with checkpoints...not, not, not the finger on map looking at map and ground and nothing else as we slowly descent towards that hill ahead narrowly missing the low flying military jet type!
Regards,
DFC
With SCA or doubble the error, there is absolutely no requirement to have a feature on track at the point where the planned track is regained.
Using the SCA, you will be back on track in the standard time. Using doubble the error, you will be back on track in equal time.
Using the 1 in 60 rule to correct direct to the next checkpoint requires you to not only spot the next checkpoint because if you don't you are lost, it also has the problem that you are now following a new unplanned track offset from the planned track. You are comprimising you safety altitude calculations and possibly separation from regulated or special use airspace.
Furthermore, since the correction you made could be for a leg of 100nm or more to destination, any further error on the new track must be assessed with regard to the new track and not against the one carefully drawn on your chart.....or perhaps you think that having calculated the errors using 1 in 60, we should use a ruler to draw in our new track and make new checkpoints?
Get back on planned track asap has to win out....so SCA or doubble error whichever.
Track crawling has it's merits in some situations. It can be very appropriate in certain situations for example keeping clear on controlled airspace. If there is a decent feature - use it. Be aware that if you use traditional navigation you could drift off track between checkpoints so you must make an allowance for that ( a buffer) when flying close to regulated or special use airspace. If there is a well defined line feature (handrail) then pre-planned track crawling along that feature can ensure safe operation.
Another example is following the coast on the seaward side as when doing so, one can disregard obstacles inland for safety altitude purposes since you will not hit them provided you don't fly inland.....can reduse enroute weather minima for the route.
However, it must be an obvious feature and pre-planned with checkpoints...not, not, not the finger on map looking at map and ground and nothing else as we slowly descent towards that hill ahead narrowly missing the low flying military jet type!
Regards,
DFC
(Dist.offx60/Dist gone)+(Dist.offx60/Dist to go) = change of heading....
The 17 and 38 were examples on a 55 mile trip. Change of heading to reach destination (but not to be on track before) would be 15 deg. Or to you, probably, 15.325077 deg......
Which is why 1/60 is NFG for pilot navigation.
The 17 and 38 were examples on a 55 mile trip. Change of heading to reach destination (but not to be on track before) would be 15 deg. Or to you, probably, 15.325077 deg......
Which is why 1/60 is NFG for pilot navigation.
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Simplest method i taught, draw fan lines 5 or 10 degrees either side of track from dep. and dest.. When off track fix position, then add the two fan lines that intersect that point. This is the heading change to reach destination.
Can be reduced to one set or even one fan line once you get use to the method
For timing use quarter or half marks depending on available features or length of legs.
These methods ok for UK terrain.
For crossing deserts or north sea...go buy a sextant, gps or Loran set!
Years ago on my commercial gft i marked on 3min points on my imc leg. when asked where i was these timing marks where spot on with my radio aid fix.
Plan a diversion...drop a straight edge from fix to div., slide to nearest vor rose, throw in a bit for wind, width of thumb 4min little cessna, 3min pa28
Also teach people to guesstimate headings without using protractor.
There are many methods...KIS.
Can be reduced to one set or even one fan line once you get use to the method
For timing use quarter or half marks depending on available features or length of legs.
These methods ok for UK terrain.
For crossing deserts or north sea...go buy a sextant, gps or Loran set!
Years ago on my commercial gft i marked on 3min points on my imc leg. when asked where i was these timing marks where spot on with my radio aid fix.
Plan a diversion...drop a straight edge from fix to div., slide to nearest vor rose, throw in a bit for wind, width of thumb 4min little cessna, 3min pa28
Also teach people to guesstimate headings without using protractor.
There are many methods...KIS.
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Chaps (and Chapesses)
I'm amazed that you can get so steamed up about "The Best" navigation technique.
The best technique for any individual is the one that works best for THEM!
I have my favourites, but as an instructor, if the student is struggling with the nav technique I teach, then I sit them down and try to find out why.
Quite often the answer is to teach them a variety of techniques and after discusuion we can usually work out which one suits the student best and then get them using that one.
Horses for Courses chaps!
Arm yourselves with the full gamut, throw away any prejudices you have about a particular method and be prepared to teach them all.
JHC
I'm amazed that you can get so steamed up about "The Best" navigation technique.
The best technique for any individual is the one that works best for THEM!
I have my favourites, but as an instructor, if the student is struggling with the nav technique I teach, then I sit them down and try to find out why.
Quite often the answer is to teach them a variety of techniques and after discusuion we can usually work out which one suits the student best and then get them using that one.
Horses for Courses chaps!
Arm yourselves with the full gamut, throw away any prejudices you have about a particular method and be prepared to teach them all.
JHC
Beagle, it's not me that's overcomplicating the method - but you & your snide remarks. You & I both know that all these heading corrections derived by *all* the methods mentioned so far are nothing more than 'good enough' approximations only.
Anyway, to use your 55nm trip & 3 nm off track example & say, 20 nm run (or 22 or 23 or 19 etc.) AND using the table I outlined above.
3 nm off in 20. Straight off that's 9 deg to parallel track (ie 3 x 3 nm).
Another 35 nm to run? Near as dammit 30 nm so that equates to 6 deg (2 x 3 nm).
All up 15 deg heading change. No difficult formula to remember.
Alternatively alter HDG 18 deg & regain track in 20 nm & the same TI it took to get off track. BTW, the table can be easily expanded for other leg lengths eg dist run 120 nm, use half the dist off as TE ie multiply by a half.
An attendant benefit is that the same distances run and to go can serve a double purpose and be used for subsequent GS/ETI checks afte the heading adjustment is done.
Yes, it can have more to it. What if you've run 75 nm? I use my whiz wheel. Unlike some in the UK, using a whiz wheel isn't considered a 'bad thing' elsewhere in the world. And no, it's not difficult or time consuming. It takes a few seconds.
I can see the benefit of your SCA in some circumstances, but certainly not as the be-all-and-end-all-there-is-no-other method. Where do GS/ETI checks get a look in? Or are you presuming the planned GS is accurate? Not much of a problem on short hops since the accumulated error is small but not a good idea on longer sectors.
If you do conduct GS/ETI checks then how do you integrate them with your SCA gyrations? It may not be common in the UK but in Oz many PPLs use a variety of a/c from 90kt C150s to 160 kt A36s or C210s. How many SCAs would you have them remember (alternatively, would you have them only ever fly at a single speed per type?)
As for some other methods:
I dislike pre-drawn drift lines because they're limited to solving a deviance that commences or terminates at the same origin as the drift lines. They fall over if the off track deviance develops at some point along track or worse, if you divert. The flip side is that if you'r adept at judging angles (or have tool for doing so. I used to have a scale rule with one printed on it), drift lines can be quick & efficient.
Proportional nav can also be useful - particularly if the proportions happen to be simple ratios. Bit of a b@stard if the ratios aren't very cooperative.
Other places I've seen had the students plot two positions & derive the actual W/V then apply that to the TAS & TR to obtain HDGs & GSs. Then calculate ETIs. Bit of a major workload enhancer but do-able & can be extremely accurate. To much bu ggerising around for my liking. Interesting to do as an exercise on very long sectors.
Jesus said it best (never thought I'd ever say that. And me a devout atheist
): It's best to have a toolbox of skills that has a variety of tools.
Anyway, to use your 55nm trip & 3 nm off track example & say, 20 nm run (or 22 or 23 or 19 etc.) AND using the table I outlined above.
3 nm off in 20. Straight off that's 9 deg to parallel track (ie 3 x 3 nm).
Another 35 nm to run? Near as dammit 30 nm so that equates to 6 deg (2 x 3 nm).
All up 15 deg heading change. No difficult formula to remember.
Alternatively alter HDG 18 deg & regain track in 20 nm & the same TI it took to get off track. BTW, the table can be easily expanded for other leg lengths eg dist run 120 nm, use half the dist off as TE ie multiply by a half.
An attendant benefit is that the same distances run and to go can serve a double purpose and be used for subsequent GS/ETI checks afte the heading adjustment is done.
Yes, it can have more to it. What if you've run 75 nm? I use my whiz wheel. Unlike some in the UK, using a whiz wheel isn't considered a 'bad thing' elsewhere in the world. And no, it's not difficult or time consuming. It takes a few seconds.
I can see the benefit of your SCA in some circumstances, but certainly not as the be-all-and-end-all-there-is-no-other method. Where do GS/ETI checks get a look in? Or are you presuming the planned GS is accurate? Not much of a problem on short hops since the accumulated error is small but not a good idea on longer sectors.
If you do conduct GS/ETI checks then how do you integrate them with your SCA gyrations? It may not be common in the UK but in Oz many PPLs use a variety of a/c from 90kt C150s to 160 kt A36s or C210s. How many SCAs would you have them remember (alternatively, would you have them only ever fly at a single speed per type?)
As for some other methods:
I dislike pre-drawn drift lines because they're limited to solving a deviance that commences or terminates at the same origin as the drift lines. They fall over if the off track deviance develops at some point along track or worse, if you divert. The flip side is that if you'r adept at judging angles (or have tool for doing so. I used to have a scale rule with one printed on it), drift lines can be quick & efficient.
Proportional nav can also be useful - particularly if the proportions happen to be simple ratios. Bit of a b@stard if the ratios aren't very cooperative.
Other places I've seen had the students plot two positions & derive the actual W/V then apply that to the TAS & TR to obtain HDGs & GSs. Then calculate ETIs. Bit of a major workload enhancer but do-able & can be extremely accurate. To much bu ggerising around for my liking. Interesting to do as an exercise on very long sectors.
Jesus said it best (never thought I'd ever say that. And me a devout atheist
): It's best to have a toolbox of skills that has a variety of tools.
The whole purpose of simplifying VFR naviagation by using SCA is to avoid having to use a whizz-wheel in flight or spend time 'head-in' looking at tables. In our crowded airspace we really don't need pilots fumbling about with the whizz-wheel when they should be looking where they're going - and all SCA work can be done head-out.
What is a 'ETI' check?
We don't require pilots to 'check' their GS, just to correct their ETAs. Hence proportional navigation is the most usual technique. Selecting such a suitable visual fix is rarely a problem - although I concede that it might be in the GAFA!
What is a 'ETI' check?
We don't require pilots to 'check' their GS, just to correct their ETAs. Hence proportional navigation is the most usual technique. Selecting such a suitable visual fix is rarely a problem - although I concede that it might be in the GAFA!
Sorry, Estimated Time Interval.
To clarify a point: you don't 'look up' the table. You remember it. I've met very few people who can't count from 1 to 4 or remember 60, 45, 30, 20 & 15.
To clarify a point: you don't 'look up' the table. You remember it. I've met very few people who can't count from 1 to 4 or remember 60, 45, 30, 20 & 15.