This is a pretty good infrared thermometer that rivals professional ones that cost many times more money (about $100 and more). It has a fixed value for the thermal emissivity while a professional one allows for an input value. Because of the natural variability of that value for different materials, the temperature readings from this thermometer can never be as accurate as better than a degree. However, that is usually good enough for checking around the house for drafty corners and thinning of insulation behind walls. The question about whether it is a 12 to 1 or 8 to 1 divergence for the detection cone is not essential for most applications that this infrared thermometer is good for around the house. I like the automatic off feature so that I don't have to remember turning it off. It does take almost a second for a reading to come up, So as you scan across a wall, move the laser beam slowly and stay at one spot long enough to get a true reading. The backlit light is very handy in dark corners too.