Calipers

There are two types of calipers:

the first one is digital. This model is highly recommended for its superior precision. It is extremely important to calibrate the final length of the reed with a minimum tolerance +or -0.25 (a quarter of a millimetre) to obtain a perfectly balanced blank. A lack of precision could affect the opening and strength of your reeds.
The second type of calipers is convenient for travel since it is small and easy to carry.