My instructor taught me a very simple "clock code" method for working out drift & GS on un/p diversions, i.e. :
Wind angle <15 deg off track, no drift & full wind speed effect on GS
Wind angle <30 deg off track, half max. drift & half wind speed
Wind angle <45 deg off track, 3/4 max. drift & 1/4 wind speed
Wind angle 60-90 deg off track, max. drift & no wind speed effect on G/S
This sounds like a bit of a mish-mash of calculating the crosswind component (say, for an approach), which has turned into something which its not. For example, the "clock code" as you call it works like this (assume wind is 20kts)
wind @ 15 deg off track. Crosswind component = 1/4 of wind = 5kts
wind @ 30 deg off track. Crosswind component = 1/2 of wind = 10 kts
wind @ 45 deg off track. Crosswind component = 3/4 of wind = 15kts
wind @ 60 deg or more off track. Crosswind component = max wind = 20 kts
I use the above all the time for approaches but never tried it enroute so I can't say that it would work in the same ratios if you are travelling at say 150kts?