To get accurate results with stock it is important to prepare your stock correctly.  To do this we want to face any side we want to have an accurate measurement off of.  This also allows us to properly fixture the material in the vise.

Below are a couple videos on preparing stock but they do not take the place of actually doing this which is part of one of the introduction classes required before using the Tomach

Squaring Stock

The feeds and speeds on this video are very conservative and slow, but the concept is good