This is a tool that is often seen in a machine shop to measure angles. I have known about them for a while, but only recently acquired one.

Things I found useful about the protractor that will make it a regularly used tool for me.

1. The protractor can be locked down to a give angle.

2. There is a broad face on the arms to make it easier place against surfaces I am measuring..

3. It was very easy to see any gaps between the surfaces and the protractor blades.

4. The protractor is rigid enough that if I do not have the angle exactly right, I press the protractor against

the flange to see if I have enough flex in the metal to do a good fit up.

Obviously name brand professional protractors can run in the hundreds of dollars, but the one I bought cost only $30 and is more than adequate for aircraft building purposes.