The British adopted "effective ceiling", meaning the altitude at which a gun could deliver a series of shells against a moving target; this could be constrained by maximum fuse running time as well as the gun's capability. By the late 1930s the British definition was "that height at which a directly approaching target at 400 mph (=643.6 km/h) can be engaged for 20 seconds before the gun reaches 70 degrees elevation". However, effective ceiling for heavy AA guns was affected by non-ballistic factors:
ఇతర అంశాలతో పాటు, సమర్థవంతమైన గరిష్ట స్థాయి కలిగి ఉండాలంటే ఒక లక్ష్యంతో ఎంత కాలం నిమగ్నమై ఉండాలి?
for 20 seconds