Blinkz,
You might find the following usefull for unplaned diversions.
I was shown this method by by a very experienced CFI/examiner and found that it works well, it takes a little time to get it into your head but once in there it is virtually as accurate as your best calculation with the wizz wheel!
first, calculate headwind/groundspeed.
If the wind is between head on and 30 degrees off, use the full wind speed and subtract it from airspeed.
if the wind is between 30 and 60 degrees off, subtract 50% of the wind speed.
If the wind is 90 degrees off subtract nothing and use airspeed as groundspeed.
EG wind 60 deg off track @30 kts airspeed 100 kts = groundspeed 85kts (100kts minus 50% of 30 kts wind speed)
You can then interpolate between these figures EG
wind 45deg. off track @ 30kts. 45deg is half way between 30 and 60 so use 75% wind speed = 22kts
the same is used for tailwind but the wind is added on to airspeed (obviously)
Then calculate drift
for wind 10 degrees off track use 10 % of the wind speed as a correction in degrees IE wind 10 deg off track at 30 kts = 3deg correction into wind.
20 deg off track = 20%
30 deg = 30%
BUT 60 degrees off track = 50%
AND 90 degrees off track = 60%
EG wind is 60 degrees off track @30kts so 50% of 30kts = 15 degrees correction into wind.
Try a few comparisons using the above against the wizz wheel, its suprisingly accurate.
I used it on my test and found the diversion aerodrome dead on the time predicted and dead on the nose.
hope this helps.