It is explained in the script that the Giga Meter is a gauge designed to measure psychomagnatheric energy in GeV's (Giga electron volts). The prefix Giga, correctly pronounced 'gi-gah' not 'guy-gah' measures 1 billion and electron volts (eV) are a unit of kinetic energy.
This prop was used in
RTD Presents: Operation Blue Line Starring The Teenage Mutant Ninja Turtles (1990)
The successful opening of the RTD Metro Blue Line on July 14, 1990 is in jeopardy when the sinister Gridlock uses his Gloomsday Device (the Giga Meter prop) to prevent commuters from learning about the fast and efficient rail service between downtown Los Angeles and Long Beach. Reporter April O'Neil calls on the Teenage Mutant Ninja Turtles (even though they're New York based) to come to the rescue and help spread the word about the new public transit system. This 10.5 minute PSA video from the Southern California Rapid Transit District features the voice actors from the 1987 cartoon as the Turtles' voices. That's definitely Rob Paulsen's voice I hear. You can watch the video in it's entirety on Youtube (the Giga Meter prop is seen from 1:23-1:48, 3:38-3:45, 6:56-7:07, 7:34-9:35) (the audio is a tad off sync).