Product review (1 stars): VERY inaccurate Relative Humidity (RH) - not even close!
Maybe I got a dud unit. Whether I did or not is irrelevant because there is no way to calibrate it. All that I know is that I received a useless piece of equipment.

Relative humidity readings were, at BEST, 20% off. Most of the time, they were 80% - 100% off (I have NEVER seen a hygrometer reading be something other than a fixed percentage off prior to calibration, so this one is REALLY broken).

I have several calibrated hygrometers to check the accuracy of this one, plus I re-checked the calibration of all of them I used to compare against this one.

I was hoping to get a hygrometer that I wouldn't have to calibrate. This is a massive failure. Unless, of course, what you actually want in a hygrometer is to not have even a ball-park estimation of the actual humidity.

EDIT: After reading more customer reviews, it seems as though a large number of the negative reviews are from people who have the ability to check the accuracy of the hygrometer (like me) and a large number of the good reviews specifically mention that they have no way of verifying the readings. The bottom line is that this unit cannot be trusted for accurate readings. I would absolutely not buy this if you have no way to verify its accuracy. I ended up replacing mine with a unit that can be calibrated, but guess what? When the manufacturer said that it was calibrated at the factory, it actually was!

Here is the one I recommend instead of the Inkbird. It's not useless or untrustworthy.
<a data-hook="product-link-linked" class="a-link-normal" href="/Quality-Importers-HygroSet-II-Round-Digital-Hygrometer-for-Humidors/dp/B000H6CZQE/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">Quality Importers HygroSet II Round Digital Hygrometer for Humidors</a>