Use the EEPROM idea but write to the EEPROM once during run time.
But before you write Z, maybe add 37 or something to it.
Now why couldn't I have thought of that.....

I went to use the rfpic transmitter the other day and the battery was flat, would the module continually be draining power with the battery in place or was it just that the battery was unused but old do you think?

Dave