This monitoring is easily accomplished by obtaining an inexpensive meat thermometer. Know at what temperature you are cooking . Your barbecue pit is different than any other. If you don't have a clue, then you are lost and have no idea when the meat will be done. The temperature of the barbecue pit affects the rate at which you are cooking.
Some pits have several thermometers to register the proper temperatures.
In controlling the heat, always keep the upper air exhaust vent fully open. The lower air intake vent should be adjustable to regulate air flow to the fire and thus regulate the temperature of cooking. Always use the cleanest fuel available . Use charcoal briquettes only when it has burned down to grey ash. Use lump charcoal anytime as it contains no impurities.