Kev31
So if its 10minutes addition 22.0 to 23.0 is 1.0 so would 22.0 to 23.5 be 1.3 or 1.5?
The addition is a fudge factor used by some schools to get a time they charge you for (the problem I assumed you were referring to); its an alternative to Hobbs time which starts counting the minute you switch on the Master Switch, so you are paying for your pre-flight electrics walk around! If they use this they will have the process written down with their charging info. For the Tech Log you simply log the Tacho as stated and take one from the other.
(10 minutes is 0.166 hrs normally rounded up to 0.2)