Once a day should be more than enough, and your ato wouldn't work as much.
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you can also do a dry bulb and wet bulb temps and do a little math, a sling psychrometer would help but not necessary, just use a thermometer with a bulb on the end swing it around and read the temp then do it again but put a wet cotton ball on the bulb this time for the wet bulb temp. just follow this guide http://www.engineeringtoolbox.com/hu...ent-d_561.html