Herpstat Question

I recently purchased a Herpstat 2 and just set it up last night. I have it set at 90 for my hot side and the probe is displaying 90 degrees. However, one of my IR temp guns is saying the temp is actually 93 and my other IR temp gun is saying it's 94. That is too hot! With the high cost and great reviews on the Herpstat I would assume it to be correct but with both temp guns saying significantly higher, I'm doubting it's accuracy. So now I am afraid to trust the Herpstat reading and am not using it. With three difference readings, how can I find out what the true temp is?

Debbie