[GreenKeys] M-28 Strip Printer

[Rokumon Cat]

Hi,
 
I want to thank everyone who has sent me photos of the M28 strip printer. I see that it has a transmission with nylon gears that the speed is selected by a knob on the front of the unit. I was wondering, what is the proper way to change speed (I will be using it at 60)? I do not want to tear up the nylon gears. Should I set it to 60 with the machine off, or should it be set with the machine running? 
 
Thanks in advance!
 
Best,
 
Joe Herdler