[ant6n]

My family's 486 had a turbo button that switched between 33 and 66 MHz, with the frequency being shiwn on the case like a digital clock.

[caf]

That screen was just telling you whether the switch was on or off, though - the logic to decide what to display was just a series of jumpers in the case front. That's why some were configured to read

  |_| |
  | | |

and

  |   _
  |_ |_|

instead. It's not like it was actually measuring the bus frequency.