Whenever I roast meat in an oven, I always use this meat thermometer. 10 degrees could be the difference between rare and medium rare. You insert the probe into the center of the meat and put it in the oven. The cable will come out of the oven door and connect to the display on the counter. The main appeal is that you don't need to open the oven and insert the thermometer to get the temperature every time, but get real time data on the meat. It takes out the uncertainty out of cooking meat. You can preset the alarm and when the meat is cooked to desired doneness, it will alert you. I set the alarm 10°F before so I can monitor the last minutes. I can put it in and hang out in the living room worry free!
Here are some numbers...
120°F-130°F very rare to rare
130°F-140°F rare to medium rare
140°F-150°F Medium to medium well
150°F-160°F Well done
But when roasting in an oven, there is carry over heat to account for. Therefore, I cook until 5°F before the desired temp. For me, I cook beef roasts to 130°F to serve at 135°F.
Chicken must be heated to 165°Fand Pork must be heated to 145°F.