what is the proper way to read the internal temp? should the thermometer be left in the meat the whole time or should you take it out after reading it and let the thermometer cool down and then take it again to see what temp the needle stops at. the reason i ask is when doing a brisket over the weekend the needle said 185 but after leaving the door open for a couple minutes the needle droped 30degs. what would be the correct temp?
Depends on what kind of thermometer you use. Most digital probes are meant to be left in the meat and read remotely while most "instant reads" are meant to take the temp as quickly as possible after removing the meat from a heat source (They'd work while the meat was in/on the heat source but you'd burn your hand).
This may be lengthy, but also may be useful. To answer your questions read the paragraph Food thermometers
When Is Meat Done? Pt. I (http://www.susanminor.org/forums/showthread.php?t=485)
Also the proper placement of the thermometer is important. Form your description of your thermometer, it appears you have a dial thermometer which is bi-metallic coil thermometers. Their temperature sensor can extend as much as 2.5 inches up the stem. If the stem is not placed deep enough into the meat, the reading can also be influenced by the ambient temperature. Opening the door will drop the cabinet temperature which could have an effect on the reading, also keep in mind, near the meat surface, the cabinet temperature can be up to 30°F lower, due to moisture evaporating from the surface. So that also could be an additional factor.