Who Needs a Meteorologist? Measure Humidity the Old-School Way, With a Sling Psychrometer!

Picture of Who Needs a Meteorologist? Measure Humidity the Old-School Way, With a Sling Psychrometer!
For some reason you just don’t trust them. Maybe it was all of the years of good weather turning to floods, or perhaps the “no more than three inches of snow” that turned into twenty inches. Maybe it’s the technology they use, or the tie they wear every night in the broadcast. It could even be that a Meteorologist made fun of you when you were a small child... whatever the case is, the result is the same and you just don’t trust them.
Good news! You don’t have to! You can make your own weather predictions by measuring the humidity and dew point of the air using a handful of household items! In seven steps, I will show you how to accurately calculate the humidity and dew point in the air without the use of a computer program or any other sort of Meteorologist trickery.

A little bit about how this instructable is set up:

This instructable contains nine steps, but step one and nine are the process overview and results interpretation, respectably. The other steps are broken down within themselves into smaller "essential" steps. All of these "essential" steps are bolded within the text and any image references are made in the first line so you can easily check the image while reading the instructions. These detailed images are complete with captions; please read them!

The text that is not bolded is supplemental and important to read the first time through. This supplemental text contains tips on how to avoid commonly made mistakes as well as the project's restrictions! If you've read this instructable before then you can probably skip reading these and just read the bold text. This setup is for your convenience.

Enjoy the instructable!
taak232 years ago
Nice piece of information. I indeed think that a software model of the psychrometric chart is even more insightful for doing first-time calculations. A free alternative to the software below which I find very useful can be found on www.psychrometricchart.net.
Julieong2 years ago
Hi nrromsey, good fundamental info to plot the psychrometric chart. There is a free psychrometric chart software that I came across at http://www.practicalpsychrometric.com/Free-Software.php There is no usage time limit. It will be good for those who want to learn more about plotting the psychrometric chart. Cheers
That chart of yours is kinda like one of those hypnotizing, spiral things (even though it doesn't move). It takes like ~ 10 seconds for me to know which one's what.
A very interesting article, but please, PLEASE make an effort to tie the string to the thermometer more securely. Duct Tape simply WILL NOT stand up to that kind of stress for very long, (in this application, the forces could easily exceed 10G and they won't be smooth and even either). Perhaps you have been lucky, but sooner or later the sheer forces will over come that adhesive, and a fragile piece of glass will be flying at high speed, in a random direction, just around head height! Consider perhaps tying and gluing your string to a piece of wood or plastic and fixing the thermometer to that? That said, hat's off to you for discussing this method and the math's that goes with it, safety is important, (I do appreciate your safety visor in the pictures) but don't stop exploring and investigating, that's what makes this site and others like it so much fun.
make a knot before you tape with duct tape. and make sure the knot is lower than the tape so that it will "catch" on the tape.
cory.smith5 years ago

As a mining engineer, we use these underground to determine the quality of the ventilating air. Very good instructable! You even cover how to read the psychrometric charts!
i0scan5 years ago
 Cool! I love the idea combining high tech and low tech and creating something like this that is mechanical but when it comes to rest there is a web cam with OCR enable to bring it back to digital.  Yeah, I am strange.  Probably looking at too much "steampunk" items on the web.