the 21J has a faux chrono. It does not work as a CHRONO. It just moves one spot each day. The above notes are correct....get either the quartz version or the 7750 versions. They are the only ones with a working chrono.
I have V3 and the main difference is the bezel numbers/and a somewhat improved date window. Other than that I'll leave it to the experts.
It's a nice one!
It's a little late. Most Ad's and Collector's I know, know all about our forums. You would be surprised. The right question should be, "who doesn't know?".