How do you calibrate a hygrometer? A hygrometer measures humidity – important for a healthy indoor climate and essential on board a ship. At Studio Maritime, we sell hygrometers with classic hair mechanisms or modern synthetic fibers. Whatever you have, occasional calibration is wise. This way, you can be sure the readings are accurate. Why calibrate? Over time, hygrometers can drift. This can happen because they've been stored in dry air, have been transported, or simply age. Hair hygrometers are particularly susceptible to this: hair dries out, which affects the reading. Therefore, it's wise to check your hygrometer once or twice a year, for example, after the winter or after transport. What exactly is calibration? Calibration means comparing the reading of your hygrometer to a known, reliable value. This can be done using another (calibrated) hygrometer, or with simple home methods like a saline solution or a wet sponge. You don't need to change anything on the device itself—unless the deviation is too great, in which case you can adjust it (if possible). Note: A slight deviation is normal. Many hygrometers have an accuracy of ±3%, so a difference of 5-6% between two readings is often acceptable. Method 1: Calibrating with a saline solution (±75% humidity) What do you need? Table salt (preferably without additives) A small bowl A well-sealed plastic bag or box Your hygrometer Here's how to do it: Mix salt with a little water to form a thick paste. Place this in the bag or box together with the hygrometer. Let it sit at room temperature for at least 6 hours. The humidity in the bag should now be around 75%. Is your hygrometer off by a few percent? No problem. Is it way off? Then you can adjust it. Additional information: With pure salt (e.g., sodium chloride without iodine/anti-caking agent) and distilled water, you can achieve an accuracy of ±0.5%. However, with regular table salt in tap water, you can get close. Method 2: The wet sponge (±95–98% humidity) What do you need? A damp, clean sponge A well-sealed plastic bag Your hygrometer Here's how to do it: Wet the sponge (not dripping). Place the sponge and hygrometer together in the bag. Let it sit for at least half an hour. The meter should now be pointing towards 95–98%. Tip: You can adjust the hygrometer while it's still in the bag. Use a small screwdriver and adjust it to ±98%. How do you adjust the hygrometer? Many hygrometers have a small adjustment screw on the back or side. Carefully adjust this until the reading is correct during one of the test methods above. Not sure? Consult the manual or contact us. Note: Do not make any adjustments until you have allowed the hygrometer to acclimatize to the test environment for at least an hour. Otherwise, you will be adjusting it based on a snapshot. What else should you pay attention to? Always calibrate at a constant temperature (not next to a heater or in the sun). Make sure your hygrometer is upright. Even temperature differences of 1°C can make a difference of 2–7% in humidity. Want to measure even more precisely? Use two methods (e.g., salt and sponge) and check whether your hygrometer measures consistently between these points. Which hygrometer is right for you? At Studio Maritime, you'll find both classic-looking hair hygrometers and modern versions with synthetic fibers . Both have their own charm and function, and are suitable for use on board or indoors. 👉 View our hygrometers 👉 Want to know more? Contact us