I have a spreadsheet (a home grown estimating template) that I want to
put a reference number in, based on the date/time, so am using =Now().
However each time the sheet re-calculates, the reference updates. I
tried using an IF to check on the value of another cell being 0 or 1
and wanted to put in a NOP (assembler term for No Operation) as the
False result to leave the contents unchanged after being set.

=IF(A1=0,Now(),NOP)

But there doesn't appear to be a NOP function within Excel.

Can anyone suggest an easy, non-VB (if possible) way round please.

Thanks in advance for any suggestions
Fred