This allows for easy checking of frame alignment using a height gauge on a surface plate. Below are a couple of albums from years ago of me using Version 1 of this tool. We are on Rev3 at this point. The main changes are making it from steel for greater durability, and thinner which makes it easier to see the gap between the tube and the “V”or step.

Frame alignment gauge -v1-flickr

Fork alignment gague-v1-flickr