It does but is it true?
Did you know that cars' tachometers are usually 2-3km / h above your actual speed and rarely show your actual speed? So if your car's tachometer shows you that you are driving at 80 km / h, your actual speed will be approximately 77-79 km / h. The basis of this is to protect you from possible speed limits and penalties. So, is it always beneficial for every sign in our life to show differently in this way? Unfortunately no!
One of the best examples of this is the hygrometers in our humidors. If we consider the effect of humidity or temperature going in the wrong direction, even a couple of degrees, on our smoking quality, we once again understand the importance of our hygrometer to show correct values. So how do we make sure our hygrometer is showing correctly? Of course by calibrating.
Calibration is a job you can do in 24 hours with a few simple materials. What is needed for this is a sealed bag, a plastic bottle cap, salt and water. The steps after setting the materials are as follows:
Wipe the cap of the pet bottle with salt.
Again, add enough water into the lid to make the salt slurry. Here, do not let the salt float in the water, but rather make it a mud-like consistency.
Put the cap of watery and salty plastic bottles in the bag with your hygrometer and lock the mouth.
After 24 hours, your hygrometer should show 75% humidity as per Roult's Law and Henry's Law *. If not, your hygrometer is out of adjustment.
If your hygrometer is an adjustable hygrometer, move the pointer to the 75 point. If not, you can note the difference and calculate the actual humidity by adding or subtracting the difference in your next humidity checks.
Calibration is that easy, but it is also an important issue. You should calibrate your hygrometer about every 6 months. I would say prefer digital hygrometers, although analogs may look more elegant. Almost all of them are sold adjustable and also have temperature gauges on them. Analogs, except for good quality ones, are generally not adjustable and can be out of adjustment more quickly.
In the meantime, if you say you don't want to mess around that much, you can use Boveda's Hygrometer Calibration Kit. With Boveda's Kit, which works with almost the same logic, you can calibrate your hygrometer according to 75% humidity within 24 hours.
After all, it is not important what your hygrometer shows, but whether it is correct. Only then can you tell if your precious cigars are enjoying or suffering in your humidor.
* - I don't know exactly how the laws of either Roult or Henry work, but as you can imagine, there is a lot of information and explanation on the internet for curious physics and chemistry geniuses.