The tramming arm is a very basic piece. Unlike using a piece of wood or other potentially crooked device, the tramming arm allows you to tram your machine with a known straight piece of material, included is (2) 1/4" metal dowel's, one for feeding into your spindle or router, and the other for finding the height difference either through the feel of resistance or feeler gauges. Then adjust your X axis, or Y axis and recalibrate. Perform as necessary. 

To assemble your Tramming Arm, just install the 2 metal dowel pins and install either one into your spindle or router. 

Do not turn your spindle or router on and rotate it around by hand.