Thanks Jerson - I will give it a go.

I presume that PBP allocates two BYTES of memory to the WORD sized variable 'RAIN' and the assembler routine only deals with one of them?

I guess I could create two BYTES to hold the RAIN data and increment the 'higher' BYTE if there is a carry from the 'lower' - Seems a bit cumbersome and I was looking for a neater/easier way.

Regards Bill Legge