If your talking about the relative humidity in your work space a couple of hydrometers would give you a good idea of your humidity. Controlling your humidity, well the heat pump or the mini split will help a lot.
Electronic humidistats are infamously inaccurate, I use them but verify them with a sling pycnometer If I know the gauge says 40%, but my sling says 50, I can use the electronic one as I know the truth.
I run a dehumidifier Holds about 50%. Dehumidifier thinks it is 45,
Pay attention to your temperature too. RH is "relative" to the temp and the amount of water vapor air can hold at that temp. As temp goes up and no extra water vapor is added your RH drops. As temp decreases and no extra water vapor is added the RH goes up. Warm air holds more, cold air holds less. Dewpoint and Absolute Humidity are other ways of measuring it.
I use an old S4 Galaxy cell phone as a shop jukebox and it has a hygrometer and thermometer on it. It has an app (Weather Station) I put on it that tracks the temp, RH, Dewpoint and Absolute Humidity and graphs it. If you use the humidpaks in your instrument case you can put your hydrometer in for a few days and see how far off your electronic meter is and calibrate it or if you can't calibrate it add/subtract from the reading to the RH the humidpak is made to keep...normally 45%. If you're shopping for a hydrometer the Abbeon hydrometers are reference instruments. They are analog so you would use them to compare against and calibrate. You can find them on ebay and auctions much cheaper than new. Personally, it's not critical to be that precise. They need to be in the ballpark for what you're doing.
My favorite hydrometer I've seen was a thin strip (~12" by 1/4" square of Oak glued to a similar-sized strip of Pine. One end was stapled to a board. The free end of the two strips would bend depending on how humid it got because of the different swelling properties of the Oak and Pine The owner calibrated it based on the weather report and marked where the free end was located at certain RHs.