I record mine in miles, converting the chains to points of a mile then round up or down accordingly for here.
I record my moves in a) a journey by journey table, detailing class travelled, TOPS, Headcode, service destination and origin, my destination and origin, the delay encountered on my journey (positive or negative) and then the mileage; b) a TOPS table detailing total mileage and journeys had behind each unit/locomotive/class; c) a Class table indicating briefly which members of each class I've had. I log by 'bashing', I don't log by sight.
My table a) entry typically would be thus;
31/12/2010- - 350120 - NMP - HML - 1650 - EUS - EUS - 1720 - -1 - 2K35 - 24.49