Build a tension meter calibration stand

After checking, the ZTTO tensionmeter chart was way off..

For 2-1.8 double butted spoke it shows 3.1mm deflection but in reality it's 2.6mm

 

The bs chart

 

The spring in the handle is responsible for applying the measurement force and it's probably not exactly high-quality. Even variation in the diameter of the bolt heads contacting the spoke will cause error. Plus the chart was probably copied from somewhere else.

Therein lies one reason for (and the beauty of) having a calibration stand.