I just bought a Croton watch, model unknown, movement as far as I can tell is a Japanese Miyota 8215, 21 jewel, unadjusted automatic. Anybody familiar with Miyota and this model movement?

the Miyota is the movement department for Citizen watch company. the 8215 is a 21 jewel automatic mechanical movement is runs at 21600 bph it hacks and handwinds. the automatic winding rotor only winds in one direction. the way the arrow points on the rotor. I can't tell you anything about the watch. other then Croton used to be a swiss watch maker, the Miyota movement are about 30 to 45 dollars. also should be day/date. I see yours is just a date,

Paul,
Thanks for the reply,It's in a display style case, screw down crown, with a silicon strap and deployment clasp, lately it has begun to lose a minute or so daily, was very good timekeeper. Appeared new or very near so when I got it. I've been wearing almost daily and I've been catching up on some home repairs, maybe I harmed it. Maybe just getting broke in and needs an adjustment to the regulator. Any thoughts?
Gary

To the best of my knowledge the miyota movement is the no 1 movement sold in the world, heard that a few times. Best thing about a watch with a miyota is it is an affordable movement to replace if ever needed and easy to find.

Yes they are very inexpensive to replace. And that is probably true. The newer 9000 models are a cheaper alternative to the ETA 28xx models. I would have it regulated first then go from there. I'm not sure how long you have had it running but it takes a couple of weeks to break in if ran everyday. I have had a 8200 miyota for about six years never been more then 25+ a day. There are a lot of little tiny parts. The automatic winding parts alone will drive you to drink. If regulation doesn't help and you decide to do the work your self make sure you take it apart very slowly. Also don't remove the detent screw all the way just enough to remove the crown.