How do you check the temperature of an oven without an oven thermometer?

I remember seeing a method that used a meat thermometer and a oven proof measuring cup w/ 1 cup of water in it. I cannot remeber the particulars of how to do it. (what temp to set the oven at and how much temp change in the water in how much time)

How do you check the temperature of an oven without an oven thermometer?

I remember seeing a method that used a meat thermometer and a oven proof measuring cup w/ 1 cup of water in it. I cannot remeber the particulars of how to do it. (what temp to set the oven at and how much temp change in the water in how much time)