After many years of trying to measure the butt transitions of frame tubes with the "sight down the inside and note the light reflections" method I decided to make a tool to do this. My designs adds almost nothing to the previous designs posted on the interweb. I have included some notes with the shots about the tool's nature. I will say here that when you think you can measure a thousands of an inch you really need to how important, or repeatable it is. Over the many thousandths (as displayed with the dial indicator) of a butt change it's easy to see where the butt changes are. More shots on this Flicker link. Andy.