Quick and easy way of measuring distance on a chart
 

Hi All,

Literally just started my nav exercises for my PPL. Can anyone give me a quick and easy way of estimating distance on a 1:500000 chart when its all folded up so no scale etc is viewable and without resorting to digging out the ruler?! For example if I have worked out that I am off track, how can I quickly work out by how much? Any advice much appreciated!

Thanks

Ben

I have a pencil with notches cut into it every 10 nm. Yes that is a long pencil ;o)

Which I use in addition to my 10 nm long thumb

Your thumb is probably around 6nm wide, OK for shortish distances like how much you're off track.

Our PA28 laminated checklists all have a 1:500 000 scale on the back, plus plenty of blank space to write on!

Otherwise, 10 mile thumb.

I also find the span of a hand, little finger to thumb is 60 nm. Have fun measuring yours. Useful for longer flight plans than a thumb (or if you are really off track)

If you have one of the vertical lines of longitude visible then measure along it. 1 minute of latitude = 1nm (don't have a half mil to hand to see what the graduations are.

Don't try measuring along the horizontal lines 'cos it don't work (unless you happen to be at the equator).

What I do though is carry a plotter with a half mil scale on it tucked into my kneeboard.

Isn't there a scale on the Frequency chart that comes with the half mil or am I imagining it?

Mike

As others have said, bend your thumb through 90 degrees, and from the knuckle to the tip of the thumb is approx 10 miles!

(now have a mental picture of FingersR measuring his thumb length :)....still, could be worse!)

tKF

Thanks everyone! Much appreciated - and yep - you just know Im going to measure my thumb now! :ok: :D

I've learned to estimate such distances reasonably accurately, e.g. to the nearest mile, just by eyeballing them.

So, FingersR get you map and with your ruler look for things (small lakes, villages, VRPs etc.) that are 2nm from something else, and try to get your eye to see that distance as 2nm. Then do the same with 4nm and then with 3 nm and 1 nm. Repeat every once in a while to re-calibrate!

To add to Gertrude's suggestion, measure the distance covered by the width of your little finger (or a biro), so you can use your finger or the biro to judge small distances. (I have a 3nm little finger and biros are basically 2nm!)

Best wishes

tp

Another nifty trick is comparing the distance to something you know on the chart -- your average ATZ is 4nm across (5nm for a large one), a MATZ 10nm across, MATZ stubs 5nm long (in the middle!), that sort of thing.

--D

Some makes of pre-printed PLOG form have a half-mil scale on the side, too.

Tim

Thanks again everyone! :D

Also handy to think of digits (appropriate with your Prune user name!) in flying time rather than having to do a further mental calculation, eg:

Thumb width = 2 minutes
1st two finger width = 3 minutes
1st 3 finger widths = 5 minutes
4 finger widths = 6 minutes

You'll have to calibrate your own hand though!

Glad to see my memory is not succumbing to old age.

There are indeed distance scales on the edges of the frequency card you get with your chart, both half mil and quarter mil.

Mike

Borrow some betting pens from Ladbrokes or William Hill.

They are 30 miles long on a half mil and 15 miles on a quarter mil
:}

Thanks All for the tips! :D

My thumb down to the knuckle is 10 nm. My span is 60 nm. What are yours?