Knowing the exact temperature of the meat you are cooking in a smoker is important. And it's also important to know that the heat inside a smoker is not uniform. One part of the unit might be 250 F. while another part might be 200 F. So what is the best why to determine the temperature?
Accurate Placement of a Thermometer
The best way to tell what temperature you are cooking at is to place an accurate thermometer near to but not touching the meat you are smoking. After all, it isn't as important to know what the temperature of the smoker is as it is to know what the temperature is right at the spot where you are smoking. This is particularly true of larger smokers. This is why most built in temperature gauges and thermometers are only good at giving you a general idea of the temperature.