https://www.rangefinderforum.com/cla...tml?1129419766
"Set the film speed by rotating the brass dial in the knob on the right side (with the meter honeycomb facing away from you, dial up); it's on a ratchet to prevent slipping, so you have to hold the knob and use a fingernail or two against the two rivets to rotate it (in 1/3 stop increments). "