You have to learn to trust your cooker. Use a thermometer with a probe on a cable so that you can put the probe inside your BBQ to keep the lid closed and still monitor your pit temperature. You can insert the probe through the meat you are cooking so it will register the temp of the air around it or put the probe all the way through a half potato so it can sit on the grill next to the meat. Every time you open your cooker to see how things are cooking you are loosing valuable heat and moisture. The best BBQ has been kept at a constant temp throughout the cooking process.