You know how thoughts drift when a good joint hits that spot
Well, I got to thinking..... Any environmental calculation is made on the assumption that the Data is accurate, this includes the data coming from the Rh sensor(s) / meters we all use. Most of us have at least one we use in our grow rooms
There is one very important thing to consider when using Rh sensors.
Calibration.
I am sure most of us growers (myself included) forget to / never calibrate our Rh Sensors. This really should be done every 6 months.
Do you trust the reading displayed, are you sure that's the correct humidity ? It is even more important if you use 2 or more devices. Now which one do we trust, if any ?
Fortunately there is an easy way to calibrate them. I do not take the credit for this method, I read it somewhere on the 'tinternet and saved it to my PC, I just pass it on.
Equipment required:
The science behind this test is that a wet sodium chloride (table salt) mixture will establish a relative humidity in an enclosed space of precisely 75%. By creating that environment inside a plastic bag, you can check to see how far off from 75% your meter is, and then calibrate it accordingly. Here’s how you do it:
- some table salt
- a small plastic lid from a soda bottle, or similar
- a zip-lock bag / airtight container
- some distilled water
1: Fill the empty bottle cap about 3/4 full of salt.
2: Pour a very small amount of distilled water into the cap, to create a slurry. You don’t want all the salt to dissolve. You want it to appear grainy and gooey, like wet sand at the beach just after the surf has uncovered it. You can pour off excess water if you put too much in, or play with the water/salt mixture to get it right.
3: Place the lid inside the zip-lock bag, then place the hygrometer(s) inside the bag, display side up, near to the bottle cap. The technically “ideal” location for measurement is suspended 3 inches above the salt mixture, but that level of accuracy isn’t necessary. Placing it right next to the bottle cap is fine.
4: Seal the bag, but don’t push any air out of it. Whatever normal amount of air is naturally inside the bag as you put stuff inside is fine. Place the bag somewhere that’s not too warm — ideally around 70F — that won’t fluctuate much in temperature.
5: If you have multiple meters put them all in together. Leave the bag overnight. At a minimum, the bag should stay sealed for 6-8 hours. Ideally, 12-24 hours would be great. You want to make sure the humidity inside the bag has stabilized at 75%
6: If the meters can be adjusted do so, If not make a note on the meter of the % it is off .... i.e. if it reads 73% when it should read 75% then mark the meter +2, that way you know to add 2% to any reading you use from that meter.
That's it.... just thought I would share.
worth a slap every time someone post this
... and the prize go's to the Frogster fro dropping the the best nugget of knowledge for the day... Bank this one people one of the best G'room hacks that can be passed on.
.
to the journal, pull up a chair 
.
(we all make mistakes).
.
