From 1970 to 1976, Shanghai Watch Factory had produced about 30000 piece of SS4 24J automatic military watch for PLA commander.
The most popular model out of the whole Shanghai Watches series. Original and mint condition is very hard to find, but I would say the original stainless steel strap is more hard to find than the watch in fact.
When you have a chance to catch this gem stone, you should check the following features:
1. the dial must original dial as well as the calendar
2. the calendar should be in red color
3. the bezel has no-crack or re-glued situation- can rotate freely
4. the crystal must have calendar window
5. the crown should lock freely
6. of course the movement should in good condition, engraved with SS4 and follow with 2 alphabet