A 30 second improvement on a 90 second time is a 33% improvement, not 67%.
Your problem is that you are need to calculate the difference in your
formula, like:
=(P21-Q21)/P21

or, use your difference result, but you don't tell us what column it's in,
so we can only guess:
=R21/P21

I don't know exactly what is causing your formatting problem. Are you using
the 1900 or 1904 date system? In the 1900 date system, you cannot display a
negative time. The 1904 date system will display a negative time, but I
don't use it, so can't tell you exactly what it does.

Regards,
Fred

"GIJoeActionMan" wrote in message
...
Hi guys,

I've formatted my cells to 'custom' then 'hh:mm:ss.00' so that bit is
fine.
The problem I have is my target time cell could read 00:01:30.00 (which
means no hours, 1 minute, 30 seconds, and no hundreds of a second), and my
actual collumn could read 00:01:00.00 (which is 1 minute).

So in my Difference collumn which is also formatted in hh:mm:ss.00 I have
made the formula:

=IF(Q21=0,"",Q21-P21)

which gives me -0.0003472, clearly not in time.

Then in my difference collumn to display the % of the difference in time,
I
have this formula:

=IF(Q21=0,"",Q21/P21)

which gives my difference expressed as a % as 67%.

If the actual is 1 minute and the target was 1 min 30 secs then I've
improved by 30 secs, so I'm not sure if this is 67% as my maths aren't too
good ?! Can I assume this is the right percentage between a minute and a
minute and a half ?

And the second thing is, why is it not expressing the time difference, and
just displaying the -0.0003472 ?!

I hope I've explained it clearly to you. I appriciate your help, thanks a
lot!