Are there any thermometers that you can put in clay ovens, or under a broiler? Most of the thermometers have a temperature limit of 350 ~ 400 degrees.  I actually burnt one down last year by turning the broiler on by accident.  
You'll want a commercial oven or high heat thermometer.  This one goes to 750° F (about 400 C):    My Big Green Egg Temperature Gauge goes up to 750° F (about 400 C).    But if I want to monitor the internal temperature of what you are cooking in a hotter oven/broiler, I usually use a remote thermometer which has an all-metal wire and probe:   