No problem, your English is pretty good

Ok so stepper is 200 steps per rev and microstepping is 10 so thats 2000 steps per rev of the motor.

I am not great with rack and pinion but I think 20 DP means it has 20 teeth in 3.1416inches so one tooth would be 3.1416/20 = 0.15708 inches. Your motor gear has 12 teeth so that would be 12 x 0.15708 = 1.88496 inches per rev

1/1.88496 = 0.53052 revs per inch

so finally 2000 x 0.53052 = 1061.0305 steps per unit.

I think

Hood