WordNet (r) 3.0 (2006):

speedometer
    n 1: a meter fixed to a vehicle that measures and displays its
         speed [syn: speedometer, speed indicator]

The Jargon File (version 4.4.7, 29 Dec 2003):

speedometer
 n.

    A pattern of lights displayed on a linear set of LEDs (today) or nixie
    tubes (yesterday, on ancient mainframes). The pattern is shifted left every
    N times the operating system goes through its main loop. A swiftly moving
    pattern indicates that the system is mostly idle; the speedometer slows
    down as the system becomes overloaded. The speedometer on Sun Microsystems
    hardware bounces back and forth like the eyes on one of the Cylons from the
    wretched Battlestar Galactica TV series.

    Historical note: One computer, the GE 600 (later Honeywell 6000) actually
    had an analog speedometer on the front panel, calibrated in instructions
    executed per second.


The Free On-line Dictionary of Computing (30 December 2018):

speedometer

   A pattern of lights displayed on a linear set of LEDs (today)
   or nixie tubes (yesterday, on ancient mainframes).  The
   pattern is shifted left every N times the operating system
   goes through its main loop.  A swiftly moving pattern
   indicates that the system is mostly idle; the speedometer
   slows down as the system becomes overloaded.  The speedometer
   on Sun Microsystems hardware bounces back and forth like the
   eyes on one of the Cylons from the wretched "Battlestar
   Galactica" TV series.

   Historical note: One computer, the GE 600 (later Honeywell
   6000) actually had an *analog* speedometer on the front panel,
   calibrated in instructions executed per second.

   [Jargon File]