First off I love fieldpiece and use/buy their instruments whenever possible. Instruments are tough becasue we have to trust them. We base everything that we think we know off of them and so reliablitlty and confidence is crucial. So... I have a dealer who did an enviornmentaly sensitve MRI scanner room. The equipment is very humidity sensitive and the dealer is using a 7.5 ton reheat rtu for cooling and dehumidification. There is apparently some type of issue there with the humidity. So we could speculate all day what it is...i'm confident that i will solve it when i go out with the dealer next monday. In preparing for the field visit i was testing/calibrating sme of my equipment and ran into a discrepancy...Name:  IMG_20120807_142544.jpg
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As you may or may not be able to see from the pictures the pocket psychrometer and induct psychrometer are side by side. both units have new batteries and have been given about 7-10 minutes to acclimate. both units are reading 76.8 DB however the induct unit is reading 38.9%RH while the pocket psychrometer is reading 45% RH. The second pic is the WB temps: 60.9 on the in duct and 62 on the pocket - pretty close when it comes to WB, right on when it comes to DB. So why the difference in RH%? 6-7% is fairly significant...which should i trust? It's a little disconcerting, considering how much the in-duct psychrometer cost me...

help advice would be greatly appreciated!