KINGZENDO JOURNAL · CALIBRATION GUIDE
How to Calibrate a Humidor Hygrometer With the Salt Test
Check the instrument before trusting it with the condition of an entire cigar collection.
Quick Verdict
A properly prepared saturated table-salt solution should create approximately 75% RH in a sealed chamber at normal room temperature. Leave the hygrometer enclosed for 12–24 hours, compare its display with 75%, then adjust the instrument or record the offset. Treat a homemade salt test as a practical one-point check, not laboratory certification.
Hygrometers can drift, including digital models. A false low reading encourages over-humidification; a false high reading can leave cigars too dry. Calibration reveals the difference between the displayed value and a known humidity reference before the instrument returns to the humidor.
What You Need
- Plain sodium-chloride table salt, preferably without additives
- Distilled water and a dropper or teaspoon
- A clean bottle cap or small shallow dish
- An airtight resealable bag or rigid container
- The hygrometer, plus its adjustment tool if supplied
The Salt Test, Step by Step
Stabilize the Materials
Bring the salt, water, container, and hygrometer into the same room. Keep them away from sunlight, heating, air-conditioning vents, and changing temperatures.
Make a Saturated Slurry
Fill the cap with salt. Add distilled water one drop at a time until it resembles wet sand. Crystals must remain visible, with no pool of standing water.
Build the Test Chamber
Place the salt dish and hygrometer inside without allowing them to touch. Keep the sensor opening clear and the display readable through the bag.
Seal and Wait
Remove excess air without crushing the setup, seal completely, and leave it undisturbed for 12–24 hours. A full day gives the small chamber more time to approach equilibrium.
Record the Reading
Read the display before opening. The reference is approximately 75% RH. Calculate the correction as 75 minus the displayed reading.
Adjust or Label
Use the calibration control exactly as the manual directs. If the unit cannot be adjusted, attach a note showing its offset and apply that correction to future readings.
Salt-Test Correction Chart
| Displayed after test | Difference from 75% | How to read it later |
|---|---|---|
| 72% RH | Reads 3 points low | Add 3 points: a displayed 66% means about 69%. |
| 75% RH | No meaningful offset | Use the displayed reading directly. |
| 78% RH | Reads 3 points high | Subtract 3 points: a displayed 72% means about 69%. |
Analog vs Digital Hygrometers
Adjustable Analog
Use the rear screw or adjustment slot gently, then repeat the sealed test. Do not force a dial that has no calibration mechanism.
Digital
Follow its CAL or offset procedure. For a non-adjustable display, record the correction rather than assuming the device is unusable.
Know the Limit of a Homemade Test
NIST reference data supports saturated salt solutions as humidity fixed points. However, kitchen salt purity, incorrect water quantity, temperature differences, leaks, and inadequate waiting time reduce repeatability.
Boveda reports that three homemade preparations measured 72%, 75%, and 78% RH in its testing. For more dependable verification, its official calibration guidance recommends a quality-controlled 75% calibration kit tested for 24 hours.
Common Salt-Test Mistakes
- Dissolving all the salt
- Leaving free water in the dish
- Allowing salt to touch the sensor
- Using a leaking bag
- Reading before equilibrium
- Testing near heat or sunlight
Test a new or unfamiliar hygrometer before relying on it, then repeat about every six months. Whether choosing a storage cabinet, an acrylic and cedar humidor, or a glass-top desktop model, verify the hygrometer independently before judging the enclosure.
Frequently Asked Questions
What should a hygrometer read during the salt test?
A correctly prepared sodium-chloride test should settle near 75% RH at stable room temperature.
How long should I leave a hygrometer in the salt test?
Leave it sealed for 12–24 hours. Waiting a full 24 hours improves the chance of reaching equilibrium.
Can I use ordinary table salt?
Yes, if it is primarily sodium chloride, although plain salt without additives gives a more controlled homemade test.
Can a digital hygrometer be calibrated?
Some digital models have a calibration function. If yours does not, record its offset and correct readings manually.
What if my hygrometer reads 72% in the salt test?
It reads about three points low, so add three points to later readings unless you adjust the device.
How often should a humidor hygrometer be calibrated?
Check a new device before use and recalibrate it about every six months or whenever its readings become suspicious.