Since in long-range naval gunnery the range-table time of flight increases with the range-table range, it would be natural to look for the shots of a salvo fired exactly simultaneously from similar guns equally elevated to splash in the order of their increasing ranges.
But occasionally one observes a shot falling later at a shorter range, or earlier at a longer range, than some other in the salvo.
The usual textbooks suggest no explanation for this phenomenon, which appears to be of no practical importance. But it may nevertheless be advisable, if only as a matter of academic interest, to try to understand the reason for such anomalies and to estimate the probable frequency of their occurrence.
But in the general case, where no special relation necessarily results between the partial derivatives, the existence of the second members in (3) prevents 8R from completely determining 8T. It is then possible for shots to fall at the same range at different times and, whenever the differences between these deviations are sufficiently large, there will be “crossed” times of flight between certain shots in the salvo.