Designing the tuning dial for the historical Radio presented an interesting human factors problem: which way should the dial rotate? I could have sidestepped the issue entirely by using a linear scale with moving pointer, with time progressing left to right (as most people would conceive of it being visualized).
Linear scale and tuning indicator- Hitachi SR-903 receiver (late 1970s)
Instead, I followed the design cues of some vintage Hallicrafters radios, with a rotating disc/fixed pointer tuning indicator.
Hallicrafters S-20R Sky Champion
-from the Antique Radio Museum
So the issue is which way should the dial rotate with respect to the dial? A discussion in Human Factors in Engineering and Design, lays out Bradley’s 1954 postulates for a moving scale with fixed pointer
- the scale should rotate in the same direction as its control knob (i.e., there should be a direct drive between the control and display)
- the scale numbers should increase from left to right.
- the control should turn clockwise to increase settings.
-from Human Factors in Engineering and Design, 308.
Only two of the three can be satisfied at the same time, so which two should I follow, to optimize the experience? One would expect time to flow clockwise, consistent with principle 2: the scale numbers should increase left to right (or clockwise). It makes intuitive sense for turning the dial clockwise to increase or move forward in time (clockwise to increase principle), consistent with (3). This arrangement violates (1)–the tuning dial rotates counterclockwise so that time appears to move clockwise past the indicator.
In Bradley’s research, this arrangement causes a number of ‘starting errors’, where the user turns the knob the wrong way initially before realizing the control-display relationship, and was ranked 3rd of the four arrangements tested.
MIL-STD-1472F states in section 220.127.116.11:
Fixed-pointer circular scale. Displays with moving scales and fixed pointers or cursors should be avoided. When circular, fixed-pointer, moving-scale indicators are necessary, clockwise movement of a rotary control, or forward, upward, or rightward movement of a linear control shall normally produce a counterclockwise movement of the scale and an increase in the magnitude of the reading.
Observing users, I noticed some starting errors, and few setting errors, as would be predicted by Bradley’s research. Overall, people found the radio easy to use and an enjoyable user experience. The clockwise/anticlockwise rotation of the tuning dial is congruent with the concept of motion of forward and backward through time, making this a good interface for the application.
Changing bands to change geographic location and theme is also congruent with expectations of users: the AM and FM bands on a conventional radio offer different content, and on a multi-band radio (shortwave, longwave) different bands provide access to the world of radio broadcasts.
-from the Antique Radio Museum: http://www.antiqueradiomuseum.org/