UK Cigar Scene Magazine September Issue 9 | Page 26

A Hygrometer Primer or
That Relative Humidity Thing
If you have your own humidor it’s highly likely that you will have a Hygrometer to measure
the level of humidity and to tell you when to add water or change your humidification
packs. Canadian Cigar lover Michael Barrett wrote this useful documentation on
humidification many years ago, but it’s still as useful today as it was back then.
I still notice that most folks are getting overly
particular about this hygrometer thing.
I believe your ultimate solution of weighing your
small humidifiers to check water evaporation, and
judging your cigars by smoking them is just fine.
A word about hygrometers; Few of them are
very “accurate”. “Accuracy” should never be
confused with “Precision”.
The only (well, one) really good way to accurately
determine relative humidity, is to use a wet/
dry bulb thermometer (psychrometer). They are
generally accurate to about 0.3% (at 68% humidity
that’s a reading of anywhere from 67.8 to 68.2 %).
Nothing else really comes close.
But it’s hard to climb inside the average humidor
and whirl that sucker around.
“Digital” psychrometers, even £65/$100 ones are
only generally good to 5% (at 68% they can read
from 64.6 -71.4% and still be “on spec”)
Cheap digitals £40/$60 from scientific suppliers
are only 5% accurate.
REALLY good digitals from measurement pros
like Omega at £230/ $350 are still +/- 3% (can read
66%-70% at 68% RH)
Scary isn’t it!
Especially for those pedantic folks who think they
can keep their cigars at EXACTLY 70%!
But a good £25/$40 analog can also give you 3%
accuracy, and does not need batteries!

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The bottom line is that if you expect a £12,50/$20
hygrometer made in China with $0.90 worth of
parts to read 70% RH when the actual RH is 70%,
you will be disappointed.
You should keep your little analog, put it in a
sealer with some just-wet rock-salt, then simply
turn the whole mechanism until it reads whatever
RH you think the salt/water gives you. (See Salt
Test Notes below)
IT’S CLOSE ENOUGH! Trust me on this one.
If you don’t want to trust me, start doing the
research. I have not even MENTIONED all the
other factors that affect the measurement of
RH, and that no cheap humidity monitor is
going to consider.
Like ALTITUDE (yep, it matters)
Like ATMOSPHERIC PRESSURE (naturally
altitude matters -Checked your barometer
before checking your RH.)
Like TEMPERATURE (that’s right,RH is
“Relative”)
Like DEWPOINT (how is the weather near
your humidor?)
Like LINEARITY ( OK this is a big point
: 99% of all these little hygrometers are