Hey BIGNORM I don't have the Avia test disc and I'm a bit confused...
Are these different test tones that are being played. ie: you get different readings with different tones?
If its different test tones then you would expect different readings at the different frequencies.
or
Is this white/pink noise being played and you get different readings during the course of it being played?
If its a full spectrum noise then its odd ( in my limited experience )you would get such variation. It really shouldn't fluctuate much at all; unless, this is the way the disc test tone is made. Hopefully someone with this disc can comment on a similar experience or not. Otherwise all I can suggest is make sure something extraneous isn't causing this, such as yourself moving infront of the metre or some thing moving in the room.
Sorry I can't be of more help, Jag
