I recently purchased a dehumidifier to place in my gun safe (product review is coming), but I wanted to make sure it was doing its job properly. The only way to ensure that is to test the humidity inside the safe before placing the dehumidifier in there versus after. And the only way to test relative humidity is with a hygrometer.

I don’t smoke cigars, but I know that cigar aficionados like to store them at a relative humidity of 70%, which makes for a wide choice in small, affordable hygrometers on the market. For my gun safe, I chose the Caliber 4R (sold by Western Humidor) based on its size (small), its looks (the gold trim matches my safe hardware), and its price (only $25 on Amazon).

Caliber 4R digital hygrometer and thermometer

The marketing blurb on the back of the box makes the following claims:

• User calibratable with easy to use digital set button
• ZX circuit technology prevents false readings
• Advanced humidity sensor maintains accuracy to +/- 1% @ 70% RH
• Fahrenheit  / Celsius switchable
• High/Low memory for humidity and temperature
• New round design with secure magnetic mount

All of that sounds great… but even after some web searching, I still have no clue what a ZX circuit is. Maybe they’re just referring to a part number of the chip that starts with the letters ZX… because that’s all I could find. 🙂

It’s small and lightweight, and feels about what one would imagine a $25 device would feel like. The body is plastic, the dial is easy to read, and I like the “analogish digital” approach to displaying the humidity.

The device came with its own battery (it takes a standard CR 2032 type) and instructions. But with only two buttons on the back, the instructions weren’t really that necessary. A few seconds of experimental pressing and I’d figured it out.

Simple two-button adjustment interface on the rear

The most important element of any measurement device, however, is how accurately it measures. So to determine that, I subjected the device to the tried and true salt test (see my separate post on how to easily perform a hygrometer salt test). I was surprised at the results. After 12 hours in the bag, the Caliber 4R was only 1% high with a reading of 76%. A couple of clicks of the buttons on the back, and the device was now reading a perfect 75%.

Caliber 4R hygrometer in a salt test

The temperature reading, on the other hand, was a tad optimistic. It was a couple degrees too high, and there’s no calibration adjustment for it. For my intended use, however, that’s not a big deal. As long as the humidity reading was accurate, I’m happy with it. If you need accurate temperature in addition to humidity readings, this probably isn’t the right product for you.

Confident that the device would give me accurate humidity readings (or at least accurate enough for only spending $25, I placed it on the inside wall of my gun safe. The peel and stick backing is attached to a silver metal disc, which sticks to a magnet on the back of the unit. The sides of my safe didn’t appear to be magnetic (weird) so I just peeled it and stuck the entire thing to the inside wall of the safe, but now I can just grab the hygrometer off the wall to check it, then magnetically stick it back on the metal disc:

Caliber 4R mounted in gun safe

Is the Caliber 4R hygrometer worth $25? No question. Of course, it’s not a laboratory grade measurement device, and I don’t feel like I can trust the temperature reading, but that’s not why I wanted it. If you just want to keep an eye on the humidity levels in an enclosed space (like a cigar humidor or a gun safe), it’s $25 well spent!