Once the crawl space is encapsulated you can begin to do what you have probably been trying to do for some time, control the conditions in the crawl space.
Keeping track of relative humidity is only part of what needs to be watched in the crawl space. It is as important to monitor the crawl space air temperature as it is to monitor the crawl space humidity. The goal is to keep the odors, mold, bugs, and what ever else you have had living down there from not living down there.
Maintaining a constant and health temperature and humidity in your crawl space will be much easier once you understand what needs to be done. I have found a great tool on the internet that helps to understand dew point. Dew point temperature and air temperature make relative humidity (RH). You will find the hygrometer most valuable once you start to use the dew point calculator and understand it. If you know the air temperature and the RH it will tell you the dew point temperature or if you know the air temperature and the dew point temperature it will tell you the RH and so on.
The most common question after a crawl space has been encapsulated is, what should the humidity be? Our hygrometer and the dew point calculator will answer that question surprisingly well.