No problem, just some information. This started with reviewing my mill setup.

I used the Mach3 Setting tab function to "set steps per unit." I am in inches and the steps came to just under 17,000 with my measurement capability.

My mill has what appeared to be ACME lead screw, but measured 0.47" and it wasn't an exact 8 tpi (normal 1/2" acme is 10 tpi, but can be had in 8 tpi)

The steppers are 1.8 degree per step and set for bipolar.

So, my first thought was that 8 (tpi) times (360 / 1.8) = steps per inch

8 * 200 = 1,600 steps per inch.

My controller is a Gecko G540, which I have read automatically micro-steps 10 divisions at slower speed which would increase the value to 16,000 steps per inch.

The 17,000 was off a bit too much. The machine is based on a German design built in 2005 in Florida by a company now out of business. The 0.47" diameter lead me to consider it was metric, so I Googled and found there is a metric version of ACME called Trapezoidal which is offered in 12 mm (0.472") and a thread each 3 mm which comes to 8.46 tpi (imperial).

8.46 * 200 = 1,692 steps per inch. With Gecko micro-stepping it became 16,920 and agreed with Mach3.

Mystery was solved.

Steve.