My Dart Swinger Project!

You'll need a dial indicator with a magnetic base. The base is 12.99 at harbor freight. It doesn't look like the dial indicator come with it. Its 16.99. Any kind of jig that you can clamp on or stick on to keep the indicator from moving will work.

Multi-Position Magnetic Base with Fine Adjustment

https://www.harborfreight.com/1-In-Travel-Machinists-Dial-Indicator-63521.html