Official Luthiers Forum!

Received my abbeon today. Looked at e bay and there are a wide variety of brands of sling psychrometer not sure which one to choose . Any recommendations ?? that you could give thanks

No personal experience but have seen the Psychro-dyne psychrometer often mentioned on the forum as being good.
Or you could just purchase 2 high accuracy thermometers, wrap one bulb in wet gauze and hold them both in front of an active vacuum hose intake. Just use charts avaiable online.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Do not get any of the antique ones. Some use actual mercury in the thermometers, and a broken one could be a hazard.

You do not need two thermometers. Get one and wrap the bulb in cloth. Take a reading when dry, then wet it and pass air over it and take the other reading. Following advice on a long ago post, I hang the thermometer in front of a fan. I read it when dry (which is most of the time), then wet it and read it when the temperature stops dropping. But you could whip it around if you want to.

High accuracy is not necessary. Look through the bin of thermometers and find some that read about the same, just to eliminate any broken ones. Pick one. The method of determining relative humidity does not require precision thermometer for luthier use. I got mine at the pet store aquarium department. I use one that is mounted on a metal plate to hang in the aquarium. Seems a little more substantial to withstand abuse, and the bulb is not enclosed in another tube.

There are rules about how fast and how long the wet bulb has to be slung. I think it is in excess of 1000 ft/min for 60 seconds, IIRC. So get two thermometers that agree with each other and let them stabilize, put one on the table, wrap the other with a piece of cotton gauze held tightly against the bulb with a rubber band, dip in water, attach a string to the other end making your hand (the pivot point) and the bulb (the end of the arc) about 6" apart, tie a loop in the end of the string, stick a pencil in the loop, and spin it about one revolution per second. If the thermometer has a plate on the back, drilling a hole for a pencil/axle right in the plate may work.

Compare the two temps and check the chart.

I have not done this for more than 10 years, so memory may be failing. This was the definition of RH for a while until tricknology came along. You will learn by checking how long the wet bulb takes to stabilize, so it may not take a full minute to get accuracy acceptable to you.

Ed