M4 and later with three pronged take up loading should reset to zero when the base plate is removed.
Origional M2 and M3 need to be reset manually:
- the M3 was designed with a removable take up spool, and if you have fitted the Leitz auto load adopted spool and baseplate attachment you still need to remove the spool to reset the counter. Although you could reload a film without a reset if you dont need the counter.
- the M2 is a manual counter, you need to remember to reset it when you load a film, unless you dont need the counter.
Noel