This is funny, I just ordered a FOSS replacement movement for the F91W, which, with a few calibrations spread out over a few months, can achieve an accuracy of <15s/yr (it also has an accelerometer and a thermometer built in). I was planning on writing some astronomy and navigation apps for it
This is great. did you leave out the alarm ringing and the continuous increment when holding the A button because they were hard to model or just to keep the demo simple?
If anybody is interested:
https://www.crowdsupply.com/oddly-specific-objects/sensor-wa...