A horological milestone each day:
The next horological milestone in electronic movements was for sure the 1971 marketed Girard Perregaux cal350 -- one year after Beta21: a quartz movement, yes but this time with stepping motor and its heart of stone buzzing at the todays standard rate of 32'768Hz instead of the 8'192Hz in Beta21.
A caliber that was cheap and pretty reliable. So, produced in zillions as cal351, cal352 ff. Thus, these later ones are around here and there, while a true cal350 is pretty hard to find -- not a big surprise since ~200 were done in a pre-production series and to a significant portion by hand, like the soldering point on the hexagonal trimmer proves. A milestone!
The photo shows a original cal350 GP produced in first quarter 1972.