Hi Dustin and welcome to the OLF!
Great story about your introduction to Kevin Ryan and many of us would kill to have had the opportunity that you and your friend had to hang out with Kevin.
Step one in understanding humidity, relative humidity (RH) for wooden stringed instrument construction is to understand that if you ignore best practices RH issues WILL bite you and often at the most inopportune time.... We see many posts from folks who's tops turn inside out or they hear a loud crack at 3:00 AM and it's coming from the direction of their shops....
What you will need to do will depend on where you live and the climate that you have to deal with as well as where your shop is located, how well it is sealed/insulated etc. Not that there are any industry standards for RH and temp but a 42-48% RH range and a temp of 70F+ are good numbers for building guitars. Martin and other fact*ries use similar numbers.
Understand in advance that all digital hygrometers are inherently inaccurate and not suitable for our purposes unless used in conjunction with a method of determining RH accurately and subsequently calibrating the hygrometer, either mentally by just noting the error, or physically for some of the better mechanical hygrometers that can be calibrated.
Do a search on wet-bulb tests and sling psychrometers and you will find a lot of information here and on the web. Either method is an inexpensive and reliable way to determine the actual RH. Once you know this you can look at your digital or mechanical hygrometers and start to understand what their numbers really translate into against a "standard" or the wet-bulb test.
I live in Michigan and in the winter I run a humidifier in my shop (and home too since they share a forced air heating system) and in the summer I am running a dehumidifier. Needless to say I am always schlepping water and hate it....
![[headinwall]](./images/smilies/headbangwalluf8.gif "Mad")
Temp for building is more a matter of builder comfort, considering the temps that the glues that we use need to perform, and understanding that many/most dehumidifiers won't work below 70F.
In a nut shell equipping yourself to do wet-bulb tests will serve you well and will help you understand that your RH may swing a great deal in the course of a single day.... It's a moving target so-to-speak but you can get control of your RH once you understand what needs to be done to your own shop area to make it stable.
Even though Kevin may have had the garage door open I suspect that he watched the RH for opportune times for cross grain gluing and other operations that can be impacted by RH swings. His climate may have provided numbers such as I noted above more frequently than my area which never.... has RH numbers in the stated range for more than a day or so....
Welcome aboard!