From the HP-35 (1972) into the late 1980s, the majority of HP handheld calculators and small desktop calculator used LC oscillators as the clock source for all the logic. That was inexpensive and precision timing was not required. Notable exceptions were the HP-55, which had a stopwatch, and the HP-01 wristwatch, both of which used quartz crystals.
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Recently I noticed that the LC oscillator circuit topology changed. In the early HP calculators, the L and C were in series; later calculators wired them in parallel.
I'm not familiar enough with LC oscillator design to know the significance of the change.
Other than the capacitor and inductor, the oscillator circuitry is contained in the MOS chips.
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These will behave completely different, in fact opposite of eachother. In series it will act as a band-pass filter. in parallel it will act as a notch filter.
@freemo Thanks! I have pretty good understanding of digital electronics, but much less of analog.