I get that question a lot as well and here is my answer which is line with TXcraig1 and Tscarborough. This mostly applies to people who just acquired an oven:
The ovens mounted with a thermometer on the door to measure the air temp provide a very poor way to measure the temperature. I can get the thermometer to show 800 F in 10 minutes with a good fire but wouldn't be able to cook a pizza. Also remove the fire or open the door and it will dramatically drop.
An IR thermometer is a good supplement but not sufficient to accurately measure the temperature. In 30 minute I can have the IR show 800 F but it doesn't mean I can cook pizza. Try to cook 2 pizza in a row or let the fire slow down and you will see the temperature drop rapidly and your pizza won't cook.
A dome and or flow thermometer that reads the temperature at the core of the oven, in the thickness of the materials is the most accurate. Once that thermometer show 700 F you can remove the fire or let it slow down and you can still cook pizza after pizza.
Used along with an IR, to make sure the floor or dome is not too hot, is going to be the most efficient way to measure the temperature of the oven.
All that said once you get to know your oven, you can tell the temperature by the color of the dome, how long the fire had been burning and so on.