Probably the best spoke tensiometer ever made. Helps to make wheels consistent.
Designed by Jobst Brandt, and unfortunately reproduced by FSA with a carbon fiber main body.
Easy to zero against a spoke and then measure tension, all with one hand. Every other tension gauge on the market measures tension across the (varying thickness) of the spoke, which requires many annoying lookup tables. This one zeroes on the spoke width, and then measures tension.