For ceramics, kilns are not fired just to a temperature. They are fired to a
"cone" level, which accounts for time as well as temperature.
Think of it as heat absorption rather than just temperature.
Cone's come in different numbers, each of which corresponds to a heating-rate/temperature-combination which will make that cone deform. At the
beginning of the firing the cone is standing at an 8 degree angle. A
perfectly fire cone will be bent to a 90 degree angle. If the cone is bent
less, the kiln was under fired. If the cone is bent more, the kiln was over fired.
Notice the way the cones are numbered. The hottest is 10, going
downward to 1. Then as it continues to getting cooler it continues at 01,
02, etc. So there is a BIG difference between cone 5 and cone 05!