Describe the proper way to measure the 'work height' ($H_w$) of a wave spring in a quality control environment.

Measuring the work height $H_w$ requires a precision load tester. The spring is compressed to the specified work height $H_w$, and the resulting force $P$ is recorded. It is incorrect to measure the free height $L_f$ and then subtract the deflection, as the spring rate is often slightly non-linear in the first $20\%$ and last $20\%$ of the stroke. The load should be measured during the 'compression' stroke to avoid the influence of hysteresis. For high-precision springs, the 'shimmed' ends must be perfectly flat against the tester's plates. Any deviation in the parallelism of the testing plates will result in an inaccurate load reading due to uneven wave compression.