Here is one of the handiest tools I've ever owned. It is a tool that I couldn't have done without when building my jeep... among MANY other projects! It is marketed toward work workers and when I bought it I was doing a lot of wood working. But it is great for great for any time you want to keep something at a certain angle in relation to another object. It has a magnetic base so you stick it to your referance surface (jeep frame) hit "zero" and then stick it to what you are measuring (pinion angle maybe?). You can also zero it to bubble level for use as a digital angle.
So what is handy in your garage?