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Random question, were physical radio buttons ever circular, or are they circular on computers only to differentiate from a check box? I've only ever seen rectan

• gumby 5y ago
  I only remember rectangular ones on actual car radios, but on other apparatus they were mostly circular. Basically a "radio button" interface is a mechanical XOR. So for example to route a signal to destination A, B, or C you'd want to push the A button and be sure B and C weren't selected. Often it mechanically latched, so you could also see at a glance which option was selected, rather than needing to have an indicator (typically a small incandescent bulb). Radios themselves implemented that mechanism slightly differently. Each button had a stop (like a tab stop, not an organ stop). When you pushed the button it disabled all the other stops and then either a spring pulled the arm right to the stop or your own muscle power pulled it left. A pully rotated the tuner dial as the arm moved right or left. I believe the buttons were rectangular in order to have enough surface area for your finger to supply a firm press enough to pull the tuner arm all the way from right to left (the extrama case). If they'd been round they would have taken up too much vertical space. The radios typically had five or six favorites, no more. The entire mechanism was mechanical.