It is likely due to electrical noise, so just ground your roaster. When my roaster is not grounded I get those wild readings, but when grounded they go away.

It's running at 240V with 2 hots, a neutral and a dedicated ground wire. I just tested it and there is continuity between the ground in an adjacent outlet in the roaster top. So yes, the whole machine is grounded.

How about installing some ferrite cores? I had erratic readings from my Huky a few months ago and they just went away. Then the other day it started again. I bought a ferrite core and wrapped the USB cable from the Phidget around it. So far it seems to have quieted down. If you're using a laptop I hear running it on the battery works.

I just tried wrapping the phidget in aluminum foil:

Did the trick:



Now I guess I'll fabricate a little metal box for the phidget and ground it.