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Just learned that the current iteration of the Caliber hygrometer, the Caliber IV is now billed as being capable of being calibrated.

As you know I've reported along with others that digital hygrometers at the consumer price point were inherently inaccurate and if accurate for a while may not stay that way as the electro-chemical reaction that they rely on breaks down over time. I've also reported that there is an issue of "range" with these too where if they are accurate they may only be accurate in a given range and outside of that range may be WAY off.

Folks who checked calibration with salt tests and other chemicals used ranges because of the chemicals that were not what we want and use for Lutherie or fine musical instrument care and keeping. One test flirts around 75% to check calibration when we want around 40 - 50% RH.

I bought two new Caliber IV hygrometers to use around my home with the hope that now that they can be calibrated I could check and calibrate these as I do my other hygrometers every nine months or so.

Both units arrived yesterday and both agreed with each other completely on temp and RH right out of the box. Problem was when checked with my psychro-dyne wet bulb testers and against my Abbeon that is my standard here the Caliber IV's were out of the box 6 - 7% RH low at 49% actual RH. This is too much inaccuracy for me and my use so I calibrated them as per the manufacture's procedure.

It's easy to do and can be repeated in only a minute or two when ever we want so that's good news.

The bad news is that the range that these can be calibrated to is only +/- 6%. I needed that entire 6% and 1% more to calibrate mine (they read low) but settled as I had to for the 6%. They work great now and I'm using them in my sunroom and upstairs acoustic guitar area. The Abbeon is still the gold standard here though.

So I wanted to report that there is a work around now in our desired range for the Caliber IV hygrometers making them more reliable for our use. YMMV if your units are more than 6% off out of the box OR there is any variance in your testing protocol. I always test twice to be sure and want both results to be very close.

Thanks

Good to know.

I'm still using one of those cheap ones as a backup that you brought up on the forum a year or so ago, forgot the name. The calibration is a red Sharpie mark on the 55% level which is really 45% tested with a Psychro-dyne

My old radio shlock digital from 1996 runs 1 to 2 percent off against the readings from the abbeon . Tnx for posting Hesh. I too am looking for a magic unicorn digital hygrometer that reads accurately . for large shop . garage , and our instrument storage room

That is good. Every cheaper digital one I have had in the past including the Caliber has read low by 6-10% and gotten worse with time.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

I like this video by Robbie O'Brien on calibrating hygrometers. His "sling psychrometer" looks like a simple to make gadget that would be handy to have.

https://www.youtube.com/watch?v=JPTU0HOPjkA

Yep I still use mine too it's a "Best Air" IIRC and hasn't drifted at all. These were less than $10 IIRC and sold by stores that sell humidifiers with the "Best Air" brand.

Out of the shop for a few months, but I thought this might be of interest. The shop manual has a section on hygrometers, and mentions that the calibration on digital units may be accomplished by adjustment of the slope of function used to generate the indicated RH, offset of the indicated RH from the sensed RH, or both. Consumer RH sensors that have a calibration feature are generally one or the other, while lab or industrial sensors may have both slope and offset calibration.

Effectiveness of slope adjustment during calibration depends on where the function is anchored...if close to where we have an interest (40-50% RH), the adjustment will not impact the indicated RH in that range, but produce large changes at higher or lower actual RH. Offset calibration produces a uniform effect throughout the range of the hygrometer, so is more likely to produce reasonably accurate readings outside of the range of interest. Adjusting both slope and offset produces the most accurate readings across the usable range of the instrument, but is not commonly seen in lower-end units.



Bovida makes calibration kits that are good for +/- 3% at the stated value, which is about the accuracy of most calibration sources such as wet bulb systems, but they also make equally accurate (inaccurate?) 49% kits...we buy the 12 x 70 gram packs for both calibration and one way shipment of instruments, but they are also available in 4 packs for $16 or singles for $6. If bagged in a poly sandwich bag, they stay fresh and usable for a couple years, so make it easy to pop into a sealed calibration box at night (clear polycarbonate sealed box works) with the shop hygrometers and verify the noted calibration 12-24 hours later.

https://www.amazon.com/Boveda-Humidity-Control-Muscial-Instruments/dp/B01B6AHW3K/ref=sr_1_3?crid=KYV3JLGXDSKC&keywords=boveda%2B49%25%2Bhumidity%2Bpack&qid=1565795711&s=gateway&sprefix=Boveda%2B49%25%2Caps%2C130&sr=8-3&th=1

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For the times they are a changin'

- Bob Dylan

That's right "Best Air" mine has been stable over the last years.

All this reminds me it's time to run the psycro-dyne again.

The big problem with battery-based hygrometers is the battery. If the battery runs low, the unit can dim slightly (hard to tell) and read horribly off. Yet it looks like it is working. Total nightmare. Mechanical just works. But if you want to risk having your guitar plates crack on an instrument, well there are alternatives to mechanical hygrometers.

Having two hygrometers solves the battery problem. And you have two hygrometers to validate each other at all times. Good insurance.

I have two digital hygrometers that always read the same or differ by no more than 1%. I check them with with the potassium carbonate method twice per year.

I bought one of those Best Air mechanical hygrometers about four years ago and it was way off reading somewhere around 60% when it should have read 43%. It went in the trash.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Have you ever had any issues with leakage from the Boveda packs during shipment? I notice in the Amazon ad, they sell a leak resistant fabric bag. Any special precautions for using these packs for shipping?

Not to date. We froze- and heat-cycled the 70g sachets to 150 deg F without any apparent harm before using them. We wrap all humidiers in microfiber fabric wrap before shipment so even with mechanical damage from mishandling, any spillage is contained.

_________________
For the times they are a changin'

- Bob Dylan

Update: I got my 49% Boveda humidity control packs in yesterday. I put one inside a large zip lock bag, along with my hygrometer. This morning the hygrometer read 50%. Looks like it is pretty close. I also intend to check it in a few days with a wet bulb/dry bulb thermometer comparison.

Yes. Or one mechanical hygrometer with no battery.

Yes, and with one hygrometer (mechanical or digital) you have no real time confirmation that the value displayed is correct. Having two hygrometers solves that problem as well.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Seriously? You're telling me that a mechanical German hygrometer tested twice a year, you are not going to know if it is correct? Do you actually know how mechanical hygrometers are used? And what their accuracy characteristics are? That's an ignorant fantasy.

Chill out. If having a single GERMAN mechanical hygrometer makes you happy, more power to you.

In answer to your last two questions: yes and yes.

I want to know that the RH values I'm reading are correct rather than just assuming they are correct based on an assumption of German infallibility, or any other sort of infallibility for that matter. I'll use my two hygrometers, you can use your single hygrometer. No skin off my teeth.

Btw, one of the digital hygrometers I use is rated at + or - 2% accuracy. The Abbeon mechanical German-made hygrometer that many hold in high regard is rated at + or - 3%.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

For digital sensors, it seems like three would be the minimum number of units to quickly isolate a faulty unit (if using indicated RH as a measure of agreement). Two digital units will not allow quick isolation of the fault unit, so will require either a calibration check at a point away from either unit's current indication or a battery swap and recheck. With an analog and digital sensor pairing, the same issue exists re: which is right, but the analog/digital pairing allows battery failures to be more quickly identified and remedied for those digital sensors that have a battery or power failure mode where the display freezes.

One effect which multiple digital units will certainly have is to reduce the probability of an undetected failure scenario, with two identical, independent units reducing the rate of simultaneous failure to about 1/1,000th - 1/10,000th of a single unit (IIRC...lots of math)...but only where the battery is excluded from the analysis!

We run a trio of sensors for easier fault isolation, and calibrate frequently (at least yearly for the mechanical and more often for the digitals, due to their additional failure modes), as well as check voltage on the digital sensor battery and replacement at nominal stated voltage.

I believe Mr. B. suggested that his mechanical hygrometers (are all of them German-made?) are in calibration, so it seems as though he is less dependent on the renowned quality of German engineering and manufacturing and more on his own reluctance to trust any instrument without periodic checks and servicing.

_________________
For the times they are a changin'

- Bob Dylan

This is pretty amusing.

First off, that you think 1% in accuracy difference makes a difference in your building guitars. The next thing which almost made me spit out my coffee, if you knew about any range measurement devices, you would know that the accuracy varies across the measurement spectrum, so the +/- number becomes relatively pointless when making 1% claim differences. But if you want to believe that 1% makes a difference in building guitars, then have at it. I've heard more ridiculous luthiery beliefs. Well ... I think I have. It's actually going to have to take some pondering. I'll have to get back to you on that.

Mechanical hygrometers are generally recommended for calibration every two years. Dead simple - you know a mechanical hygrometer is range accurate if you've calibrated inside that time frame. No need twice every six months, or multiple battery hygrometers to believe somehow one informs the other for accuracy. It's just nonsense advise for those that don't know better.

And for those calibrating, make sure you calibrate around the humidity level at which you build - that's the accuracy that matters. The accuracy at 60% RH is meaningless.

That said, I believe we arrived at no and no. I'm chill, heck, laughing repeatedly! Thanks for the entertainment!

Whatever. Happy trails to you, pardner, and may you always get everything you deserve.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

On the other end of the equation is how closely your humidification/ dehumidification equipment controls the humidity. In order to do that it needs to be hooked into some sort of humidistat, which normally will allow a range of humidification before turning on or off.
I try to build instruments at the appropriate humidity levels during critical parts of the construction, and monitor the the humidity with a reasonably accurate method. Fine tuning your controls to the "Nth" degree is still no guarantee that the guitar will never have humidity induced problems - we don't control where they live after they have left the shop. Hesh informed us that the caliber IV hygrometer was now able to be calibrated, a plus for those who like to use a relatively inexpensive digital hygrometer. Thank you for that information.

Clay, I'm in your camp. As a hobbyist, I want my guitars to last so I'm doing other things, building necks and making parts until the weather cooperates in the fall. When the normal humidity comes down so as not to tax my dehumidifier, I'll get the RH down as low as I can get it. If my hygrometer reads 30% and it's really 45% then I'm good. Once my critical work is done I'll shut the dehumidifier off or set it to cycle on and off until the next critical phase. In the end, I'm not going to worry if my hygrometer is off by 10%, it still gives me a good feeling when I look at it and I know i'm in the ball park. I have many other things to spend my money on.

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Hutch

Get the heck off the couch and go build a guitar!!!!

Clay, I'm in your camp. As a hobbyist, I want my guitars to last so I'm doing other things, building necks and making parts until the weather cooperates in the fall. When the normal humidity comes down so as not to tax my dehumidifier, I'll get the RH down as low as I can get it. If my hygrometer reads 30% and it's really 45% then I'm good. Once my critical work is done I'll shut the dehumidifier off or set it to cycle on and off until the next critical phase. In the end, I'm not going to worry if my hygrometer is off by 10%, it still gives me a good feeling when I look at it and I know i'm in the ball park. I have many other things to spend my money on.

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Hutch

Get the heck off the couch and go build a guitar!!!!

I bought this controller (TCH-1) for my humidifier/dehumidifier many years ago and it has worked flawlessly. It is light years better then the controllers incorporated into the machines themselves. It has remained accurate within an acceptable range as correlated with my Abbeon and a sling psychrometer.

http://old.greenair.com/humidistat.htm

I think the current offering is the TCH-2

http://greenair.com/atmospheric-control ... controller

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It's not what you don't know that hurts you, it's what you do know that's wrong.

I agree - we control what we can control, and educate the owners of the instruments we build or maintain so that we minimize the RH-related repair work we see as a result of those instruments residing outside that control. There is no perfect solution which I can see, only acceptable-, better-, and best practice, with associated costs in equipment, overhead labor, and resultant acceptable risk.

The boss got a chance to look at a new Western Caliber IV sensor mentioned by Mr. Breakstone, and the calibration mode appears to provide offset of the digital readout, versus adjustment of the slope of the function used to generate the displayed RH value. This seems like the preferred mode of calibration for a sensor which will see use across a very large range of RH values, versus a narrower range. I don't believe I would depend on a single example as the sole RH sensor in the shop, but I can certainly see 2-3 units backed up by another reference method to handle the battery issue or single-model failure modes discussed earlier (the Lufft units marketed by Abbeon or Cole-Parmer are readily available on the used market for 1/3-1/2 new pricing, and as covered by others, there are other models or brands of sensors) . I also might think about scattering a few around the shop, as we routinely see 2%-3% variation in calibrated shop RH between back storage area, machine area, and the two bench areas (with that variation making me far less concerned with the 1% difference in claimed accuracy between some units). We have additional mechanical units distributed throughout the shop, but some digital units which can be compared to the 'master' trio of RH sensors might do nicely.

I should mention that both of the boys in the shop were originally advocates of digital sensors over mechanical devices, and after both experiencing the unique failure modes associated with digital electronics, now advocate a mixed technology approach (e.g., mechanical with digital backup or digital with mechanical backup, depending on the shop).

Also, while some of our customers have willingly spent thousands or tens of thousands of dollars on environmental control for their collections, that is too much to expect for those that routinely travel with an instrument or have just one or two instruments of modest value to protect. For these customers, a single low-cost, reasonably reliable digital sensor might be the best approach to monitoring home, hotel, or case RH.

_________________
For the times they are a changin'

- Bob Dylan