Histogramming all 50-ish resonator frequencies shows reasonably good distributions:
Notably, there’s no obvious suckout in the middle, as with those eBay Hall-effect sensors.
I don’t know what to make of the difference between the
parallel series-capacitor and basic serial resonant frequencies for each tuning fork:
Perhaps each resonator’s frequency depends on its (laser-trimmed) tine mass and follows a more-or-less normal distribution, but the
parallel-serial difference series capacitor changes the frequency based on (well-controlled) etched dimensions producing quantized results from three different masks / wafers / lots, with the motional inductance and capacitance incompletely modeling the physics?
For reference, the resonators look like this:
Producing the histograms uses the LibreOffice
frequency() array function, which requires remembering to whack
Ctrl-Shift Enter to activate the function’s array-ness.
[Update: Faceplant about “parallel” resonance, which is actually the shifted resonant peak due to the 24 pF series cap. Apparently I typo-ed the second histogram subheading and ran with the error; the figures are now correct.]