It's actually quite easy to measure inside and outside tube diameters w/ a vernier calipers (they have seperate jaws for ID and OD measurements as shown in the pics. If you need to measure deeper into a tube, there are spring loaded inside gauges that you insert into the tube, allow to expand, then lock and remove, and you measure these with your calipers or micrometer. Unlike the $70 tool, this technique will allow accurate measurements of intermediate diameters rather than just a few steps, and you can use the tools for all other measurements. But if you want another single-use bike tool, go for it.