Calipers: $9.99 and up
Tape measures are great for carpentry, but they lack the precision to be accurate enough for RC use. Calipers are the perfect alternative as they are still small enough for the toolbox, but have the accuracy to record crucial setup parameters. They can be used to measure the diameters of tires, ride height, spring preload and toe. They are accurate to.001″ so you can be sure that your setup sheets are accurate and repeatable. Calipers come in both mechanical and digital readouts. Both styles are equally accurate, but the digital versions usually have a button to switch back and forth between imperial and metric units.