My detector has become erratic, no clicks until I touch it, and one high reading when I touched the tube to ensure it was seated OK (GMC-200).

I just looked at your chart.

1. Try a full reboot of your computer.

2. Try a new data cable.

3. If you have a backup GMC200 to connect, I'd suggest that.

When your unit is giving readings, they seem to be in the normal range most of the time. Most of your erratic readings fall to zero so maybe there is a loose connection on the GMC200 motherboard or maybe a bad data port/cable connection. Having a backup geiger counter works as a great way to trouble shoot your problem. Plus in the event that you get high radiation, you can verify quickly that your readings are correct.

It seems to be related to the detector. Clicks/flashes stop, then start when I touch it. The last recovery was due to just touching the negative end of the GM tube with my finger, it seems. Maybe I'll re-solder the connector.

I had one giving erratic spikes once. I wound up removing and resetting the GM tube. It seems to have solved the issue. In the process I bought another 200, 300E and a few extra tubes. Overkill? Not for me and my philosophy of two is one and one is none. Anyway, cheap insurance. For what it's worth.

I had never heard that before, but I like it! In my life I have found it so helpful with troubleshooting things when having bought two of them.