The most common use of a 3D printer is to enhance some tool/object or make a replacement part. In this cases accurate measurements play an important roll on this act of reverse engineering/enhancement, and you'll need a proper tool to do this. The must-have tool is a Vernier Caliper.
With this tool you can take measurements with great accuracy, we're talking about into tenth of a millimetre in the most basic models. This tool is mandatory in any t(h)inkerer tool case!
|Animation of a caliper measurement using a vernier scale.|