Ir reflects and flexwatt is shiny this will lead to false readings. Most ir guns are calibrated to be looking at something roughly the colour and reflectance of a brown paper bag everything else is off somewhat. The allowable deviation of this ir gun is about 2ºF up or down (the PE1 is the best sub 200$ gun I have found at 1.5º +/-) So 5 degrees off is not a big surprise. The deviation on the herpstat probe is very low .3 I believe. IR guns are really not very accurate under the correct circumstances they can be ok. but that is it. Get a GOOD thermometer (mercury lab grade or platinum probe traceable digital but sit down when you look for a good (.5º accuracy digital one it will scare you. some LC ones are also very good and are cheap. Just check the packages on the shelf if ten or more read the same you can expect a .5 degree accuracy. To test this for your self flip the flexwatt over for an hour or so so the herpstat probe is on the carpet away from drafts and them quickly move it and check the carpet it should be with in 2 degrees. Don't take my word for it CHECK the SPECs and email Dion at spyder Robotics he will tell you the same thing.
Alex