Is it possible to set up data validation to allow only numbers greater than
or equal to zero OR text equal to n/a.

I have check sheets for machine maintenance with specific tests listed and
cells formatted to accept results. These results are numeric (=0) but there
are some machines without certain options fitted so some checks are not
relevant. I would like to allow the user to enter n/a in these cells if the
check is not required.

Any ideas?

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Ian
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