Subtracting Times

[Knawl]

I am making a timesheet but having trouble with subtracting times.

I have subtracted 3 times away (start time / lunch break / end time) to calculate hours worked.

I have then taken this from the Contracted hours to see + / - time worked.

However when you look at the calculation of the + / - time worked as a number, there is a a variance at the 16th number past the decimal point when they should be exactly the same (for 07:35 - 07:35). This causes the timesheet to display + and - values for 00:00.

Please see attached excel file on the Example sheet dates 26/01/2011 to 27/01/2011. I have no idea why there is this discrepancy.

Many thanks.