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.