Confirms the clamping pressure required to read correct frequencies on the DigiFlex? Frequency Meter. Clamp the shaft firmly, oscillate & read CPM's displayed in the meter's digital readout. Adjust clamping pressure & repeat the oscillation steps until the CPM's match the exact spec frequency. Trains you how to repeat the correct clamping pressure to ensure 100% accurate frequency readings. Frequency Spec Shaft can be used to compare the accuracy of other frequency meters.