In 1973, Citizen launched its first quartz watch and named it Crystron. This was in response to Seiko’s Astron of course and the two brands competed well into the next decade across model genres.
In 1975 only one such example was the Citizen Crystron Diver, but there were may dress variants and lots of other more different models analog and digital, with alarm, without, but all the way up the scale right to the Crystron 4 Mega.
With the precisely adjusted AT crystal and rated at +-3 sec/year, this ultra accurate very labor intensive, very expensive model with caliber 8650 of which only 3000 were made was Citizen's flagship watch. Depending on the work put into these watches one can also find 4 Mega's rated at +-5 sec/year or +-10 sec/year.. The "cheaper" SS 4 Megas used the 7370D movement, based off the 7300.
This leaves the "ordinary" Crystron as the entry level watch, well suited for the everyday wear and tear in the Japanese office environment. Like the Lord Quartz and possibly the spoofier King Quartz of the late eighties with caliber 9923. Nevertheless, they are still great vintage pieces precisely because of that usage history. Try finding a Crystron, or a Lord Quartz for that matter, in reasonable to good condition as a survivor of the quartz craze era.