Caliber IV Hygrometer Accuracy

Edited: August 21, 2017, 8:51 PM · I have read through the archives and realize there are many threads on hygrometers but I thought this was worth sharing for those in need of one or in search of a better unit.

I live in a relatively dry climate with a humidity level averaging 22% to 35% (sometimes as low as 19% ) in summer and when in the single digits to -30F winter (most of the winter). I had previously been trusting an analog hygrometer that came with one of my cases, which I realize are notoriously hit and miss for accuracy, but was ok with it for my then current violin. That changed when I started looking for a better upgrade violin.

After much research I decided on a CaliberIV calibratable hygrometer. I later found on this forum that this is the same hygrometer that David Burgess sells. Reportedly very accurate and and with excellent reviews from other instrument and humidor sites, especially for the price point.

The CaliberIV comes precalibrated but I didn't trust that so I bought a Boveda 32% RH level and a 75% RH level calibration kit, being that the manufacturer says that salt calibration will cause corrosion to the unit as well as it being less accurate. I checked with the facility that calibrates our instruments at work and they verified that salt calibration by itself and using consumer table salt will vary from 72% to 77%, with most people thinking it to be 75%.

I first used the 32% RH level kit and let it set for 24hrs. The CaliberIV indicated 31%, so I left as is and then used the 75% RH level kit, waited another 24hrs and the reading was spot on 75%. Very impressive for the range involved. Regardless, while apparently calibrated and very accurate from the manufacturer, I would not trust all to be received as accurately calibrated. The odds are against it.

Several weeks of use and being transported in my case has demonstrated the CaliberIV to remain stable in calibration, as I repeated the calibration check a week ago with the indications remaining the same.

If this subject has been beaten to death, I apologize.

Replies (24)

Edited: August 19, 2017, 4:29 AM · Skip, the IV hygrometers tend to be pretty close right out of the box. I calibrate the ones I sell, so what I've found from calibrating a large number of these is that there will be a few outliers which are so far off, that I just throw them away, assuming them to be defective and not worth messing with further. The vast majority though are within plus or minus 3% of a correct reading (a total range of 6%). Among the various inexpensive brands I've tested, that's about the best I've run across so far.

I realize that nearly all brands will claim accuracy within this range, but as you have already found, most of these claims don't mean anything. I've tested some which were more than 20% off, including some which claimed to have "NIST traceable" calibration, or be for "scientific" or "laboratory" use.

As you pointed out, the Caliber IV also tend to hold their accuracy well, drifting very little over time. (That's another area where some brands fall down badly.)

August 19, 2017, 12:09 PM · Lesson learned David,that I could have saved my research time by just checking this site first. You had already done the work and I could have just ordered it from you.
Edited: August 19, 2017, 12:33 PM · Skip, please don't look at it that way. You did some good and valuable independent investigation. And we all (hopefully) know that people who are selling something can't always be trusted.
August 19, 2017, 3:06 PM · Guys, I did the same with no difference in results. Inexpensive test, just to be on a safe side. Thanks for recommending it David.
August 21, 2017, 11:03 AM · @ David Burgess
Do you ship your tested Caliber IV hygrometers to Italy?
I might buy one on Amazon for about 43 euros, but I do not want to get into one of those that are not good (as you say you've found few times) and did not even want to buy all the calibration equipment to know that it doesn't work.....
August 21, 2017, 1:21 PM · No, US sales only. Export requires too much time and paperwork. I try to do what I can in the humidity control arena, without it taking too much time away from my making, and without charging a lot
Edited: August 21, 2017, 1:24 PM · Double post.
August 21, 2017, 1:40 PM · What luck! I popped over here to check out what's been going on, and the hygrometer that I just purchased is being discussed! Very excited that I picked "a good one". I have one of those analog dial ones that is perpetually stuck at 60%... time for an upgrade.
Edited: August 21, 2017, 3:15 PM · @ David Burgess
Well, then I just have to hope to find the good one, to add to my collection,but I suppose it will not be a real problem.
Thank you anyway for the information you provide on your website on this subject, very interesting and useful.
August 21, 2017, 8:49 PM · David S., If you are able to purchase from Amazon in Italy, then you can purchase the Boveda calibration kits for around $8.00 US. If you want to keep it simple and adequate, just buy the 32% RH kit. They are simple one-step kits. Break the seal, open the pouch, turn on the hygrometer, place it in the pouch and seal it. Wait 24hrs and read the hygrometer display while in the pouch. If the reading is more than 1% or 2% off, recalibrate using the simple instructions that come with the CaliberIV. It will take less than a minute to recalibrate. Then place it back in the pouch and check it again in 24hrs.

Having an engineering background and due to the nature of my work, I'm a little anal, well ok, according to my wife, a lot anal with a good measure of OCD thrown in, so a 1% variance is about all I can tolerate, but 2% or 3% is good enough for most, so don't get to carried away or you'll find yourself chasing your tail. Compared to most of the hygrometers in most violin cases, accuracy within 5% or 6% would be a huge improvement. For the price point, simplicity, accuracy and ability to calibrate, these hygrometers are hard to beat.

August 22, 2017, 3:17 AM · Yes, I think I will also buy the calibration kit, it is worth spending, also because I have many other hygrometers to check.
I tried to check with saturated salt solution but the corrosion issue is somethings which is best to avoid.
August 22, 2017, 7:54 AM · Yes, it is, and the salt method apparently isn't as accurate. The Boveda kits are also reusable for several months.
Edited: September 12, 2017, 3:53 PM · I finally purchased my CaliberIV hygrometer on Amazon for 40.45 euro and the Boveda calibration kit 75% for 6.26 euro.
Unfortunately the 32% calibration kit is not available in Italy and Amazon does not ship it from abroad so I had to give up for this.
I tested the hygrometer with the kit and after 36 hours it read exactly 75%, it would also be interesting to test it at the lowest percentages but I think I can feel satisfied about the accuracy.
Nice little tool.
September 12, 2017, 10:32 PM · That sounds pretty cool... Davide, you'll have to show that to me! :-)
September 12, 2017, 11:22 PM · Corrosion issue? You are not supposed to immerse the hygrometer in the salt solution! The salt is not going to jump out of the solution and march towards the hygrometer. But I guess that as a company that wants to sell calibration kits it is smart marketing.. ..
September 13, 2017, 1:42 AM · Hi Dimitri,

whenever you want, I will be in my workshop compatibly with my lessons at violin making school, that by now are not yet definitive and may change weekly....
Maybe call me by phone or whatsapp or email

Edited: September 13, 2017, 2:01 AM · @ Bo Pontoppidan

Probably you are right, but Boveda calibration kit it's actually very practical and fast to use, costs a little and is reusable.
I also have some Magnesium Chloride that I probably will use for 33% RH test, but I don't know if it will be reusable more than one time.
Some clue?

PS Anyway, since I'm not a Boveda advertiser, here is the list of salts to use for test at various percentages of RH:

September 13, 2017, 5:36 AM · @BoPontoppidan, with the Boveda kits you are not placing the hygrometer in a solution but in a plastic bag with a dry Boveda test pouch. I talked to several violinist who use the Boveda kits and have had no corrosion issues in several years use whereas they did have some issues using straight salt. FWIW
September 13, 2017, 1:58 PM · I was just saying that testing with salt solutions there I not going to be a problem with corrosion since you basically do the same thing - place the hygrometer next to a saturated salt solution inside a sealed container.
September 15, 2017, 2:21 PM · Bo, there does seem to be a difference between placing some hygrometers above a saturated salt solution, and using a moisture-permeable membrane in between (like Boveda does, and like I do). I'm not enough of a chemist to explain why, but my hypothesis is that some of the salt somehow makes it into the water vapor in the air, without the membrane.
Edited: September 15, 2017, 6:12 PM · There is not any salt (NaCl) in the water vapor. If there were, then one would not be able to remove salts from water by distillation.

If you use tap water to make your solutions then there could be some chlorine (Cl2) present, which can enter the vapor phase. The chemistry of chlorinated water is actually rather complex. The folks who make the test kit probably use distilled water.

September 16, 2017, 4:53 AM · @ David Burgess

May I ask what kind of membrane do you use for this purpose?
Does normal paper or perhaps filter paper work?

Edited: September 16, 2017, 10:53 AM · Davide, I got some samples many year ago that I am still using. I think it was bulk material for making reverse-osmosis water purifiers.

I'm not sure what other materials would work, but for something inexpensive, perhaps Tyvek house wrap would work? I haven't tried it...

Paul, I can't explain what is going on, but when I've tried putting some types of hygrometers in a chamber without the barrier, they didn't work right after that. Household chlorinated water alone was fine. Do you have an explanation?

Caliber 4 says that the Boveda packs are fine for calibration, but specifically states that suspending above a salt solution will damage the hygrometer and void the warranty. Any thoughts on why this is?

Edited: September 16, 2017, 2:22 PM · Dupont Tyvek home wrap seems promising, but I don't think I can get a small piece for my own use.
Maybe I can cut a piece of Goretex from my mountain jacket and see if it work.... :)
Even if probably recycling an exausted Boveda envelope should be cheaper and the best option.

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