I never gave it serious thought until now but the Giga Meter isn’t described very well in the script and thankfully not as it would have been in the feature film. It’s pronounced ‘guy-gah’ but the prefix Giga is correctly pronounced ‘gi-gah.’ Also the script says it measures in GeV’s, which is one thousand million electron volts. A Giga measures one billion which would have been easier to say than the former and electron volts are kinetic energy units. This device doesn’t present itself with the same simplicity the PKE Meter does (a personal invention of Egon and Ray which could be described as a more refined EMF meter tuned specifically for psycho kinetic energy and the like).
I’ll still refer to the Giga Meter the way its pronounced in the film as I’m sure that’s how Ramis and Aykroyd wanted to make it their own but it’ll always be in the back of my head now knowing these truths. Kinda similar to the 1.21 jigowatts (gigawatts) deal in Back to the Future eh?
While this has all been dicussed a few times before, I’m lost as to what you’re talking about in the last paragraph. Giga is pronounced “Guy-gah”, always has been, even outside of Ghostbusters dialogue.