It is rather unusual for a hygrometer that costs less than 200 dollars to come with an individually-numbered certificate of calibration. This one does. However, since it only comes with a single-point calibration (23C, 46% RH), I checked mine at other values of temperature and relative humidity. Temperature was the easy part for me to check: first I calibrated a digital thermometer in an ice-water mixture and in boiling water, then I compared this device to that thermometer (I couldn't directly test this unit in water because unlike that thermometer-only device, it cannot be immersed and also this device only reads up to 50% C). For humidity, I used the only calibration method that doesn't require kilobucks worth of equipment: the classic salt solution method. Put the probe into a sealed container above a saturated solution of NaCl in water, and the RH should be very close to 75% (after a suitably long time for stabilization). Above a saturated solution of MgCl in water, the RH should be very close to 33%. At all temperatures I tested, and at both values of relative humidity that I tested, this device came well within its stated specifications of +/-1 degree C for temperature and +/-3 percent RH mid-range to +/-4 percent RH elsewhere. I do not have the capability of testing the accuracy of barometer readings.

I did notice as I was comparing temperature readings that my other digital thermometer responded much more rapidly than this device did to changes of temperature; this is to be expected because the temperature-humidity probe of this device is physically much larger than the simple temperature-only probe of the other device. So when only temperature is needed, a simple thermometer-only device is preferable.

For humidity, this device is reasonably accurate; to get significantly better RH accuracy one would have to spend a substantial amount of money.