Calibrating a Hygrometer:

Since the hygrometer is our only visual indicator for what the exact RH level is inside the humidor, I recommend calibrating your digital hygrometer twice a year and replacing the battery annually (weak batteries can give a false reading as well).


How to Test and Calibrate a Hygrometer:
1. Fill a small container with salt (milk bottle cap or ketchup cup works well).

2. Add a few drops of distilled water. NOT enough to dissolve the salt, just enough to moisten it. You want the mixture to be thick and pasty.

3. Put the cap inside of an air tight zip lock bag or plastic container along with your hygrometer. Then seal the bag or container. (Tupperware works well).

4. Wait 24 hours, then check the reading on your hygrometer without opening the bag or container (or quickly open the container and check if the container is not clear).

If the reading is 75%, then your hygrometer is accurate and no adjustment is required.

If the reading is not precisely 75%, then you will just have to remember to add or subtract the difference between the test reading and 75%, in order to determine the actual humidity level inside of your humidor.

For example, if your hygrometer test reading was 80%, then subtract 5% from the readings you get when the hygrometer is inside of your humidor to determine the actual levels of humidity. (e.g. a reading of 70% inside your humidor equals an actual humidity level of 65%).

Writing the +/- percentage on a piece of tape or small post it note and affixing it to the hygrometer works well.

I hope this helps and happy smoking!

~Mark

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Appreciate the advice. Here's a pictorial representation of how I'm going about it:

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This hygrometer is being calibrated for this humidor:
http://www.cigarasylum.com/vb/showthread.php?t=21025
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Thank you for the informative thread. I can attest to this hygrometer calibration method. I have done it a couple of times already and all went well.
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I have a Nappolion II Humidor, it came with a fancy looking analog hygrometer. I tried calibrating it with the steps I read here.
After 24 hours, the hygrometer read 45%. It has a flat head screw on the back, and when I turned it to adjust the level to 75% the whole thing spin in its casing, I eventually got it to 75%.

Also, I am currently seasoning the humidor. I filled up the humidifier, and placed 3 small bowls of distilled water, one in each drawer. I did this about 32 hours ago, and I placed the hygrometer in the humidor at the 24 hour mark.

The hygrometer currently reads 85%. Is this normal while seasoning? or is my hygrometer just malfunctioning. I plan to buy a digital hygrometer soon before I dare to put any cigars in.
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A good move, Richard, as analog hygrometers are notoriously inaccurate. It migh be hard to say what your current RH actually is, could just be the hygrometer.
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Question. Maybe I'm missing something but it takes at least 24 hrs to get the hygrometer up to 75% Rh in a very small sealed environment. So can't we expect the hygrometer to take just as long to read the Rh in your humidor? The reason I am asking is my humidor is 69% Rh with more than enough (65%) beads in it. I just calibrated my hygrometer 2 days ago and was wondering if the hygrometer needs a few days to drop to the range of the humidor.
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Howdy.

Digital hygrometers can be off even after calibration. I've seen "drifts" from +/-1% to +/-10%.

The RH Beads also have a +/- 2% range, so this may explain the 69% reading (+2 on both accounts).

Additionally, weak batteries can account for inaccuracy in hygrometers as well as the quality of the hygrometer. One NIST cert. hygros are dead on but they run in the hundreds of $.

Opening and closing your humidor as well as adding and removing cigars can affect readings as well.

I hope this helps

Mark
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well it's been a couple weeks, and my Humidor is sittin on 70%, 70 degrees, right where I wanted it!

I wanted to thank all that helped out while getting my box where it needed to be!
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Just curious, what is the importance of having the salt dampened and not saturated? Does it affect the RH? For instance, if the salt is saturated with water, will it not produce the ideal 75% RH?

And how specific is this? Are we talking a big difference between the two?
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Too much (or too little) water can change the results slightly but since most common hygrometers are only accurate to within +/- 2-3% I think that as long as you have "salt saturated with water" and not "water with salt added" that you are OK.
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alright, thanks.
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BTW, I should add that the Boveda Calibration packs are mighty easy to use, relatively inexpensive, no-muss-no-fuss, and if you keep them in a small sealed container they will last for quite some time...
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true, but I'm short on funds atm, I already have salt :-)
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I am doing the salt test on two hygrometers in the same bag. They are reading about a 5% difference in both of them. Any suggestions on which one to trust? Should I only be doing one at a time?
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Trust 75% to be accurate. Adjust your hygrometers accordingly. The more the merrier in the bag.

Oh temperature will have an effect on your Relative Humidity. Try and calibrate around 70 Degrees F
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This really good information. As a noob I had noticed the calibrate on my hyd but had not idea how to use it correctly.
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Being new to this and reading stuff for a couple of weeks now, I wound up doing the salt test with my analog hygrometer that came with the Humi.

Somewhere I thought that i read that you only needed to do this for 6hrs or so, at least thats what I had in my ind when at the 7 hour mark I took it out of the bag and put it in the Humi.

Anyway, when i put it in the bag and sealed it it was reading approx. 60% it slowly went up to a reading of 74% by approx. hour 3 and stayed there until i took it out of th bag at hour 7...do you folks think that is acceptable or should i start over and do the entire 24hr cycle?
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I would recommend you get a digital hygrometer as the analog hygrometers are notoriously inaccurate. Just my :-)
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That is the plan, probably order one tonight or tomorrow so it will probably be late next week or the following week before it arrives.
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If you have a local B&M shop, my advice would to buy a few sticks from them and have them do it. Definitely +1 on the digital upgrade.
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