Thank you all for your responses.

FSt1 Entries in cells will not change

HTH Your formula returns the error "A value is not available to the
formula or function".

Tyro The formula works very well . Thanks. If you have the time, and
inclination, would you post a word description of the formula - I cannot
follow it entirely.

Biff The three answers are 'no', but your formula returns the same error
"A value is not available to the formula or function". I tried to follow it
through but stumbled on the double quotation marks inside the final
parentheses. What do they mean? Should they have something between them?

Regards, Ken