An angle finder is a tool that has one purpose, but a couple different styles of operation. Deciding which one you need to utilize will require some basic knowledge of the tools function and what job you are intending to do with it.

One style of this tool works in a scissor-like fashion. A hinge holds two straight edge rulers at any angle between 0 degrees and 180 degrees. When at 0 degrees, the two rulers lay upon each other, and when at 180 degrees, the rulers form a straight line and can be used very much like a yard stick. The angle of the hinge can be adjusted to mark any angle you may need at which to cut something, attach something, or complete any of the other various carpentry actions.

The second type of tool is the protractor style. This tool is basically a tool with a solid, right angle base, often magnetized, and a wheel on top with the various degrees of a circle marked out along the wheel. This one works by placing the angle finder in a right angle joint, like a door jam, and moving small levels in the circular part to find any various angle you may need.

Since the majority of carpenters are highly concerned with making sure all their joints are "plumb, level, and square", the protractor style is better designed to check right angles and construct things out of right angles. Whereas the scissor style is better suited to joining different materials at any angle you may need.

As with most things in carpentry or construction, do make sure that you "measure twice and cut once." One may even wish to measure multiple different times, just to be sure of himself and not waste any materials.

As per usual with internet research, if you plan on purchasing an angle finder, you should utilize the various search engines and do some reading and research before you buy anything.