There are three different measurements for the rate of fire: cyclic, sustained, and rapid. Cyclic is the maximum rate of fire given only mechanical function, not taking into account degradation of function due to heat, wear, or ammunition constraints. Sustained is the maximum efficient rate of fire given the time taken to load the weapon and keep it cool enough to operate. Finally, rapid is the maximum reasonable rate of fire in an emergency situation when the rate of fire need not be upheld for long periods.