How to Calibrate a Hygrometer

Basic Growing Info
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I just learned this yesterday and wanted to share. I also learned that my crappy ProTherm hygrometer measures 4% lower than it should.

  1. Place the crappy little hygrometer into a zippered plastic bag.
  2. Take a soda bottle cap and make a thick paste of table salt and water in the cap. Make sure the paste goes to the top. If there is standing water on top of your little cap full of slurry, use a paper towel and dab it off.
  3. Put the hygrometer AND the cap with the salt/water paste in it, inside of your zippered bag.
  4. Seal it up and read it 24 hours later. It should read 75.5%.
  5. Note the difference in your hygrometer and go to town.

Also note: most hygrometers have a margin of error of 5%. So make sure to factor that in.

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Those plastic bags have micro pin holes in them and leak.

Try a plastic container with a sealed snaptop type lid or you could double/triple bag your setup.

How do I know?.. :smile:

I went through all of that when I ran the salt test on a batch of those cheap hygrometers a couple years ago…

Cheers
G

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I have like 50 of them…just lay them out toghether, pick the ones reading the same, close nuff for me that way

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There’s a ‘relative’ humidity joke in there but I can’t parse it out… :laughing: :vulcan_salute:

Cheers
G

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:boom: :rofl:

Thanks for looking out for all of us @navy66 !

:fist_right: :fist_left:

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This has been a great convo. And wow, I found a few people who think a lot like I do. :slight_smile:

Thanks all. Keep your roots dry! But not too dry. :wink:

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I may be wrong but shouldn’t there be a temperature offset for this test?
Would the RH inside be the same at 90F vs 65F?