HP48G Clock Variability

[TomC]

As we know, the processor clock of the HP48 has a bit of apparent variability. The hardware multiplies the installed 32.768kHz crystal to about 4MHz. (one finds this when doing the <ON><D>A test.

Has anybody studied or understood the source of this variability?

It is either due to:
1. The precision of the installed 32.768 kHz crystal.
2. The code that produces the apparent clock frequency.
3. The accuracy of the PLL that performs the multiplication of the crystal frequency.
4. Other source?

While I suspect it is 3, it would be nice if it is 1, then a replacement of the crystal would solve this variability.

TIA,
TomC