
The gauge is Quality Importers Hygroset II, ~$10 (it was $15 when I first bought it). It's designed for humidors and its claim to fame is that it is a digital hygro that can be adjusted. Really easy, too! Calibrate as usual, make a note of how far off it is, and turn the little knob that many "clicks" (very faint, but noticeable) in the right direction. Then press the little black button on the left to accept the change. I like this feature so much, I got a second one. The red button up top switches between celsius and fahrenheit. The unit has a magnet on the back and a little metal plate with adhesive that you stick to the wall (I have mine on a popsicle stick, so haven't tried the magnet).
I'm always on the lookout for the smallest gauges. Here are a couple of more currently in use:
Accurite suction cup thermometer, ~$6. I like the size, only 1/2" thick! It's easy to read, and I like that it has min/max (resets every 24 hours). I only wish it was a combo gauge or that they made a matching hygro! I saw what is probably the updated model at Lowe's the other day.

Mini Power-Free Hygro, $2.74 and free shipping all the way from China, LOL. This was so inexpensive that I threw it in my Amazon cart, then forgot about it during the month it took to arrive. It calibrated within 1%. Hubby says it's probably adjustable, but there doesn't appear to be an easy way to do it. It doesn't come with any way to mount it (I've got it taped to a popsicle stick).

I originally started with this no frills Flukers analog combo gauge, ~$8. I wanted to love it, but the hygro is way off, can't be adjusted, and worse, the spacing between the numbers changes proportion so the lines are REALLY close together in the higher range. I marked where the needle was when I calibrated it so at least I know where 75% is, but I don't trust it. The thermometer is accurate, though.
Smaller is better for me, but I like fancy toys, too. Has anyone tried a wireless gauge, where you put a sensor in the tank, and have a large, easy to read unit outside of it? Like the reptile or aquarium gauges that have a wire you put in the tank, but without the wire and with a bigger display. For multiple tanks, here is a "cadillac" version (with a cadillac price) with three sensors that can tell you the temp and humidity with min/max for all your tanks on one display!