Triggering Macro 1 time only on change of cell value

[yidrasil]

Folks, as an inexperienced excel programmer/user I'd appreciate help with the following problem;

I have an application that updates the text string in A1 every x minutes (time may vary). I'm trying to develop a toutine that will trigger a Macro/call a function/subroutine once only on each change of data (and then not trigger again until the next change...and must only trigger on change of data in this specific cell). So the timeline looks like this

start A1 = "Apples", Fire macro once

start + 10mins A1 = "Oranges", Fire Macro Once again

start + 25mins A1 = "Pears", Fire Macro Once again

etc.

Triggering the macro is no problem but constraining to one triggering is proving a problem (for me anyway) and is really holding up my application progress.

[darkyam]

This is cross-posted here: http://www.ozgrid.com/forum/showthread.php?t=86315

[shg]

yidrasil, please read the forum rules about cross-posting.