If you want to use a formula, you would need to go to
Tools=Options=Calculation tab and click the iterations checkbox to allow
intentional circular references. Set max iterations to 1

assume if cell A1 has a 1 in it, you want B1 to show the time it was placed
there

=IF(A1=1,IF(OR(B1="",B1=0),NOW(),B1),"")

use a custom number format under Format=Cells and use hh:mm:ss.000

another approach would be to

select the cell and do Ctrl+Shift+: (colon)

Or you could use a macro.

Sub SetTime()
Activecell.Value = Now()
End sub

--
Regards,
Tom Ogilvy






"Girlie Bloat" wrote:

I have set up a formula in Excel to record the time for riders in a bike race
who are doing a number of laps. Each time they come over the line I want to
put their race number in to a cell and for Excel to record the time. I have
successfully created a formula to do this (if the value of the cell into
which I put the race number is 0 the time is inserted into another cell).
However, once the time has been inserted I don't want it to change when I put
another race number in to the cell below. Does anyone know how I can do this?
Sarah