Since I had the feeling that my analog hygrometer/thermometer broke (I'm pretttttty sure the humidity in my tank didn't suddenly drop to 20%), I decided to buy a new, digital one from my local Petsmart. There were a lot, but the one that caught my attention was National Geographic's Thermo-Hygrometer. The actual digital part sits on the outside, which I think may be important since the high humidity in crab tanks may affect the wiring or something if it stays in there for too long. Not to mention that if it were in my tank, it would be very hard to read with all the mist on the glass! There are two probes which hang off of it that go into your tank that do all of the work. The whole thing is very aesthetically pleasing, which to me is important (gotta get that tank looking as good as possible!)
A very nice feature of this device are the battery trays and spare battery. They don't mention this on the packaging, but on the back are two trays (kind of like disc trays on your computer) that can be pulled out and small watch-like batteries can be placed inside. I was disappointed to find that the batteries had died on mine, until I realized that the second tray holds a spare battery just in case the first one runs out. Very convenient! The device only needs one battery, but since they usually come in pairs when you purchase them, you might as well refill the spare battery container when you can.
I calibrated the hygrometer and was pleasantly surprised to find that it quickly went to 75% and stayed there. I don't have a second one, but I think the accuracy of these devices is quite good, especially in relation to other hygrometers (I had one once which was 10% off!) The only problem is that if it is off, there's no noticeable button that I can see which lets you calibrate it. However, even if it were off I doubt it would be more than 5%, in which case it's quite easy to just add/subtract the difference. If you want accuracy, this is the device for it.
Lastly, though maybe not as important as other aspects of my review, it is a nice touch. There's a clip attached to the device which you can see on the picture, making it a strange "T" shape. It's used for if you have a National Geographic tank, in which case you can attach it directly to the rim of your tank. Since I don't have one, I was worried that it it would have to sit awkwardly on it's back -- but that's not the case. You can take off the clip, and if you look at the back of the device there's a little fold-out plastic piece that let's it rest perfectly upright anywhere. So don't fret if you don't have a NG tank! This device works fine without one.
All in all, this is a great thermo-hygrometer, and I strongly recommend it. It's pretty, accurate, and has many neat little features which just add to its perfection overall. It's also not a bad price at $19.99 USD (however I got it on sale for $14.99 CAD), and though it looks a little expensive it's definitively worth it. The only part I can't review is how long it lasts, but presumably it'll last longer than any of the cheap analog ones I've bought in the past. So if you're looking for a new hygrometer, then give this one a chance -- I did, and I don't regret it a single bit.
