What is the X in X-mas?
An instrument for indicating the speed of a vehicle, typically by measuring the rate of rotation of a wheel or fan whose rate of rotation depends on the speed of the vehicle. Compare odometer.
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.
instrument that indicates the speed of a vehicle, usually combined with a device known as an odometer that records the distance traveled.