How to measure moisture in crawlspace

[Zac P.]

In a few of my rental properties, the crawlspaces have a lot of moisture and mold in them. I have a plan of attack to deal with the issue, but I'm looking for a specific tool that you all would recommend to measure moisture/humidity in the crawlspace? I'd like to carefully monitor the moisture to make sure that what I'm doing is actually helping. Thanks!

[Matt Clark]

@Zac P. you need a hygrometer.  You can find thermometers at home centers for about $20 that also have a hygrometer built in.  It will measure the relative humidity (RH) and track the high and low readings for a 24 hour period.