I have noticed that the hand held Temp gauge is always off by 30 to 40 degrees compared to the On Board Unit.

I tested on different engines and the results were the same. Like eveybody knows the Hand Held Temp gun has to be as close as possible to the glow plug center by pointing it from the top of the heatsink. In all the tests the On Board device, to put down a number, would be 270 while on the Gun the readings were 220.

I dont think the OFNA T Gun is damaged or not calibrated, its just reads about one to two inches away because the crown does not let you read any closer. So, everytime you tune with the gun always add about 30 to 40 degrees specially during break-in.

I know the unit is not damaged because I have a cooking probe inserted on the automobile's A/C vent. In the digital display the reading was 62, on the cooking probe about the same and in the OFNA temp gun just a 2 to 3 degrees off be it a little lower or higher.

It makes sense the MIp or VENOM device installed on the buggy or stadium truck reads more accurate because is as close as it can be for making accurate readings. So far following the 30+ rule for temp gun readings has worked well for me.