Gerry, once again I like your use of rare earth magnets. More of a rather clever measuring device, or gauge, rather than a tool. I was hoping to see some new tool to adjust axle position without first properly putting bike on a stand so the tire is off the ground. Rag still works between sprocket and chain to move axle forward. However to move axle rearward with the new extended swing arm I find myself needing an equally extended pry-bar to fit between tire tread and front of swing arm.
Nice prototype, thanks for taking time to make and share video with us.