Most manufacturers only list their straightness tolerances over a specified length. I believe Easton' s are for only 28 inches of the shafts.

Spin testing is done for assuring your broadheads (and in the old days, glued on nocks) were true to the shaft. You don' t need the gauge for that. You can eyeball it. Spin the arrows on the rollers and see if you can detect any wobble at the tip of the broadhead.

Good luck.