Part I – Using Boveda to Calibrate Hygrometers

Editor’s Note: This is not a paid endorsement of or a solicitation for any of the products mentioned in this article and 99 Cigars neither sought nor received compensation from any brand or company whose products are featured.


We’ve been there many times: breathlessly moving humidors to cooler or warmer areas of our homes and/or constantly adding / removing Boveda packs to adjust to our ideal RH and having a stroke when we discover dried or wet cigars. Or worse – mold and beetles. Yikes


The most challenging aspect of safeguarding our precious cigars is keeping them in an ideal environment, an environment in which the proper temperature and humidity, or Relative Humidity, are critical for their care and feeding. If you’re like most of us, getting both of these elements just right – if that’s even possible – can at times be an exercise in futility many times over.


Fortunately, newer technologies like  2-way humidity control, digital hygrometers and even old tech items like calibrated thermometers can be a huge help in taking some of the guess work out of storing cigars properly and that also means mitigating costs, worry and of course, damage to our beloved stogeys. In this 2-part series, we explore some simple, effective and relatively inexpensive ways on how everyone can get a handle on measuring whats going on in these environments and more importantly, just how accurate that information really is.



Whether  you’re a wily veteran or novice, an aficionado or casual smoker, sorting through the myriad of options and brands to keep our humidors humming can be overwhelming. Compounding the challenges are the equally numerous reviews, advice and opinions  – from helpful to head scratcher – from a number of sources that at times  seem to even contradict one another. Well, we’re going to try and strip all this down to bare bones and help you make some educated choices based on science and objectivity.



Our initial focus is Relative Humidity, or just RH: that wonderful vaporous state that keeps our stogeys from becoming kindling. Naturally, we desire a tool to measure RH as accurately as possible and any number of branded analog and digital hygrometers are up to the task. Personally, I eschew the analog versions as I’ve yet to see one that isn’t wildly inaccurate.  Now, it’s important to understand the difference between accuracy and precision because while some of our measuring devices can be precise, they may also be inaccurate and vice versa (see the guide below). By the way, the last target on the right is a depiction of neither accurate nor precise but we thought the alternative caption was funnier and yet sadly, true.




We have 10 digital hygrometers in use around here, including one for the sole purpose of measuring ambient RH in our office. Most are Western Caliber IV, but we also have a couple from Xikar and Humi-Care. The Caliber IV is a fan favorite and from a price and reputation standpoint, offers the best reported accuracy available; however, it is important to note we’ve discovered that all 10 hygros differ in RH values from -1% to +3% RH. So, while this could be considered accurate, as a group precision is lacking. Temperature differences, however, are all over the place and will be the focus of our next installment in Part II.




Western Digital Caliber IV Digital Hygrometer



We’d all love to assume that these hygros are spot on right out of the box, but the fact is they just aren’t. A 4% RH difference in a group of 10 hygrometers may not sound terrible, especially when you consider individually most were within 1-2% RH. Not bad, but not great. Here’s the big “but”…a couple of them were off by 3% RH (low) and when you’re trying to hit a sweet spot of 67 – 69% RH, that could falsely read anywhere from 64 – 72 – that’s a range of 8 RH. This makes calibrating them an absolute critical step in getting your set-up right from the start.


While electric, climate- and humidity-controlled cabinets are great (and comparatively expensive), it’s still imperative to properly normalize or calibrate them as they too can be affected by, among other things, ambient conditions causing RH and temps to wander. So, even with automation, you’re not out of the woods. I can’t emphasize this enough: You will always need to rely on the info provided by your calibrated hygrometers and sensors.


So, how do you calibrate your hygrometers?




© Neptune Cigar

 Well, most of us cut our teeth on floating a teaspoon of table salt and distilled water in a bottle cap followed by a few hours in a sealed ziploc or tupperware bowl. Good times. This is based on the premise that a salt and “pure” water in a saturated solution will maintain a constant RH in a sealed container (see Raoult’s Law and Henry’s Law). In this case, a saturated sodium chloride (NaCl) solution produces a constant RH of approximately 75%. Unfortunately, there are 3 problems with this. First, distilled water does not even come close to being “pure.” Second, getting the salt and water concentrations right is near impossible – yes, it matters. Lastly, temperature affects RH, so setting your sealed bottle cap next to the radiator isn’t the best idea.



Purists will disagree and espouse that this method has always worked for them and I fully stipulate this is a fast and dirty way to at least get close under the right conditions. I’d rather be as close to the bullseye as possible so I turned to my old friends at Boveda for some help. I’ve been extremely happy with their 2-way humidification control products (again, this is not an endorsement) and lets face it, I’m not quite ready to part with $350 for the PEM2 Datalogger from the Rochester Institute of Technology that was designed for measuring RH in museums, libraries and archives.


While not alone in the 2-way humidification game, Boveda produces a convenient all-in-one kit for under $10 that has garnered a lot of attention. Utilizing a single 8-gram, 75% RH humidity pack and a resealable packet, it doesn’t get much simpler or cheaper. Instructions? Meh. Drop in your analog or digital hygro, seal ‘er up and let it sit unmolested for 24 hours. Done.







We calibrated all 10 of our hygrometers including one of our newest gadgets, a Cigar Scanner temp/RH sensor. I’m happy to report that most of the hygros/sensor were within 2% RH with a couple that were spot on at 75%. Unexpectedly, two were off by 3% RH. After each calibration, we programmed the margin of error in each hygro and marked the individual hygros on the back with a -/+ and the RH number they were deficient. For example, our Humi-Care model in the left photo read out at 76% RH, so it was marked with a “-1.”


While this exercise is pretty straightforward and cost effective it’s important to not overlook a couple of things. First, all our hygrometer batteries are checked and replaced annually at a minimum. Calibration of your hygrometers should not be a “one and done” activity and should be done periodically throughout any given year. If you’re a casual cigar lover with a a couple of small humidors, once or twice a year should suffice whereas an aficionado or collector with an expanse of rare and expensive cigars, might want to calibrate more often.


The Boveda One-Step calibration kits run about $8, give or take, and are available at all the popular big box stores (including Amazon) as well as your favorite tobacconists. Once opened, Boveda claims it is reliable for up to 3 months and recommends calibrating within a stable temp range of 65-75 degrees F. I would simply reinforce the guidance of keeping it in an area of your home that doesn’t experience extreme temps, huge swings in temperature or in a sunlit window.



RH Confirmation post reprogram of +2% RH margin of error (24 hours)


Combined with monitoring the temperature, a reliable, calibrated hygrometer is a powerful tool ensuring that your cigar stash remains in tip top shape without all the fuss and worry and without putting a huge dent in your bank account. This should be done in concert with other best practices like regular rotation, beetle inspection and even “dry boxing” prior to smoking. The whole idea is to dial in your monitoring tools closer to that ideal accuracy and precision bullseye and with the Boveda One-Step Calibration kit, you’re there. – In Fumo Pax!

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