Problem with time formula

[Gary]

I am building a spreadsheet that show a start time and a finish time. I then
want it to calculate how much over the allotted time was used if any. I use
the formula (a2-a1)-30. 30 minutes are the allotted minutes so it looks right
that this formula would give me the correct amount of minutes over. I get the
###### error message on this and I can't find a way to get it to give me the
correct time. If I take the -30 out of the equation it will give me the
total time. I can I get the total time minus the 30 minutes?

 

[Dennis Tucker]

This should work....

Format columns A,B,C,D for Time(13:40 format or whatever)
in A1 put "0:30"
in B1 put starttime("0:00" format)
in C1 put stoptime("0:00" format)
in D1 put "=C1-B1-A1"

Dennis