Remember, when a screw has a spec of .004" per foot it means the real accuracy is LESS than that amount. If it was more it would be out of spec and presumably the manufacturer would not ship it.
I am curious what instrument you have in a shop that can measure to an accuracy of .004 per foot? maybe a 10" micrometer? How would you set it up to make a table movement measurement?
My point is guys get all hung up over screw accuracy, when lots of other factors have as big, or bigger influence.
The 'calculate steps per in' button was added because so many people seem unable to understand the math involved in the calculation.