The fast traverse is a completely separate interrupt handler, precise placement only happens at speeds where the motors can handle an instantaneous reversal.

There is more work to do. When it encounters back lash it will tend to trail by the tolerance and I will need extra remedial steps. OTOH I'm not going to try to fix anything until it has had a chance to tell me what needs fixing.

I'm writing the code and everything runs in SRAM. I can recompile and upload all new in a matter of seconds. I am in control