Review on AikTryee 4-Pack Mini Digital Thermometer Hygrometer: Precise Indoor Humidity & Temperature Monitoring Gauge 🌡️ with LCD Display Fahrenheit (℉) - Ideal for Humidors, Greenhouses, Gardens, Cellars, Closets, and Guitar Cases by Matthew Coste

If you are using these to check the humidity in a humidor I would recommend taking all 4 and placing them in a plastic bag with a small bottle cap soaked with salt and sufficient water in the humidor is. Salt. Seal the package. Wait a few hours and see which ones are closest to 75% read. Those that do are best for reliable measurements in a controlled environment (humidor). The rest can simply be used indoors for an "overview" of humidity. None of the 8 options I tested were very different, but some (most) were on par. You can also test them with the standard moisture pack, which is guaranteed to deliver a certain percentage. Like 72%. They are inexpensive and generally very accurate. Good seller and decent product.