[time-nuts] Any guesses as to how Citizen is claiming ±1 second/year with using this AT-cut 8.4MHz XTAL?

[Dan Rae]

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 :^)

Dan