Fortunately, there is a way that a complex shape can be measured accurately no matter how strange the curves or turns. All that is needed is an object to measure, an ink pad, and some centimeter graph paper.
First thing to do is get an object that needs to be modeled for printing. In this example, a drawer guide that has an arm broken off will be used. If it were fixed, this piece should be identical on both sides. This piece has lots of complex shapes and measuring it completely would be a challenge.
A good candidate for the grid paper method is a piece that has at least one flat side, or that can easily be made to have a flat side. The back of this piece is not flat at all, but the front has only two nubs sticking out that would be easy enough to remove. Just note their location before removing them since they'll need to be modeled back in. Then use a sharp blade and cut them off.