Answer
In a Crest-to-Crest wave spring, not all waves may be active if the end turns are squared and shimmed. Active waves are those that contribute to the deflection; inactive waves are those in contact with the loading plates or adjacent shims. The spring rate $k$ is inversely proportional to the number of active turns $N$. If the ends are 'flat' (shim ends), the number of active turns is $N - 1$. Failing to distinguish between total turns and active turns results in a theoretical spring rate that is lower than the actual measured rate, typically by $10$-$15\%$. In high-precision aerospace sensors, this discrepancy can lead to calibration failures. Precise design documentation must specify the number of waves per turn $n$ and the exact count of active turns to ensure rate accuracy.
