I would like to calculate time differences within Excel but am having trouble with the formula.

I am comparing a screen time to the actual speaking clock time.

e.g. Speaking clock = 13:00:00 System time = 13:05:00 Difference = 00:05:00

The problem I encounter in Excel is when the calculation is reversed:

e.g Speaking clock = 13:00:00 System time = 14:55:00 Difference = -00:05:00

Excel refuses to calculate this time difference and just shows ######, it can't seem to handle the minus calculations for time. I'm sure it can, it's just me.