1/10 of an hour. Not sure if this is changing with all the time tracking software now but it's easier to bill by tenths than it is to track/calculate exact min

1/10 of an hour. Not sure if this is changing with all the time tracking software now but it's easier to bill by tenths than it is to track/calculate exact minutes and any larger unit might involve too much rounding up. e.g. .1 for a quick email reply is more palatable than a .25 (1/4 hour, 15min) minimum.