Way back in 1960 something Braun in Germany made a little alarm clock using a 4.194304 MHz crystal which could reach this level of accuracy.  I had one and it certainly met the Harrison level of timekeeping when I used it for navigation.  I think that the crystal cut used had a temperature coefficient at room temperatures that had minimal variation at around this frequency.   Way better than the 32+ kHz crystals used now.

The clock died in the end but I still have the crystal somewhere :^)


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