"Off" and "On" conditions
The dial scale is light and spring-loaded so that it has a very fast action, and "snaps" quickly as it rotates from one state to the other when you turn the on/off knob. The Motorola 41D is a battery-only AM portable radio from around 1940, in the "suitcase" style cabinet. It was important in battery radios to have a good power-on indicator, since batteries were expensive (operating costs were typically 4 to 20 cents per hour, in 1940 dollars). Most sets just had a red dot in the tuning dial to indicate "ON", so this dial set the Motorola apart from the many other suitcase portables of the period.