Thanks , Hmmmm logicaly it's seem good but it did not work .....I found the right number for my Acme 5/16-14 treaded rod ....it's 398.00 step per mm, maybe 400.00 but with all the other setting when I print a calibration bloc it's the best I can go for exemple a bloc of 10mm are with this number 9.97 high wich is ok for me now .
So thanks for your help and every day I learn more and more ....it's part of your knowlage, thanks you
Marc .