I just wondered why some 2x3 crowns have a top button and some have a side button for opening. Russ

Russ,
Not unique to the 2x3...found on the 4x5 also! Simple answer, model to model improvements for problimatic features
...example, the old style tension hardware was a real pain for repairman when tensioning the curtain, and it was felt that a governor was needed as well...both problems were solved and simplified at the same time! I doubt if anyone but a repairman really appreciated the difference except for the cleaner appearance and easier settings!
Have a nice day...Bert