Many thanks for you very clear and informative answer .
You are 100% correct.
I had thought the crystal I was using was around ±30 PPM but as it turns out its ±100PPM going to change the cryst ...
This is my second ever post so please go easy on me.
I am using code posted by ckielstra on a 18F4525 in a clock/timer application
The problem is that I am get some timer driff not much it equates ...