I have a Shopmaster Eldorado. I was cutting a rectangle on the mill and ran into a problem so I got out the dial indicator and coded G0I Y 1.000 and it moved 1.0000 but when I coded G01 Y0.0000 It moved 0.9830. This makes one side shorter than the other of course.
The machine has ball screw leads on all axes  and there does not seem to be very much back lash.

any idea how to correct this? ? ?

Sounds like you may have your steps per unit set slightly wrong for he Y.
Hood

ball screw leads on all axes  and there does not seem to be very much back lash

First make sure you have the steps per unit correct via calculation or use the axis calibration feature. Then check that it moves correctly by making a move to remove any backlash, and now make another move in the same direction to confirm that the setting is correct. Then check and measure the backlash by going in the opposite direction.

RICH

May be worth checking that you do not have a loose coupling between your motor and leadscrew (check grubscrews etc.) also check that everything else (leadscrew nut etc.) is tight.

Tweakie.

thanks Guys, , seems it was a combunaion of both. I was supprised at the back lash though. I sure didn't feel any thing in the screw. Guess this old millwrite is loosing the touch