I think this fits here - it's probably not high tech enough to be considered "metrology".
Since the topic of little rad detectors has come up again, I figured that I should post some pictures of the one that I made a few months ago (not to mention that Doug has requested it too), which is a little larger than a cigarette lighter. I loaned mine out and have been waiting to get it back so that I could get some better pictures, but for now I'll post what I have.
This is the circuit board minus the GM tube which is a Russian surplus unit. It runs on a single 3V 123A battery. A few things that make it different from some of the others that are similar is that it has a LED bar graph display with the first green LED flashing every count for low level stuff and the last red LED about half lit on the hottest torbernite rock that I have. There's a button for the power switch and a 3 position slide switch that changes from clicks/nothing/vibrate, a la pager motor.
This is the unit with the cover off. The GM tube is in front and about 1/4" diameter by 5/8" long.
And the final product. It's 1" wide, 7/8" thick and 3-3/4" long.