summing h:mm column for timecard sheet ?

[Sven Crouse <svenc snet net>]

I have two columns formatted as h:mm representing start and stop times
for work.  I can subtract the start time from the stop time for hours
worked that day, but when I sum a column of "hours worked that day" and
that value > 24 then I increment the day.  Is there a way to get total
hours for a h:mm formatted column ?

Sven