Why main and secondary batteries corrected fire differently

Do modern railguns need many barrels for salvo ranging, and does gun size affect how many shots are needed?

Modern targeting reduces the need for large ranging salvos; historically, slow-loading heavy guns fired, checked, and corrected, while faster secondary guns corrected during continuous fire.

Traditional battleship gunnery had time to observe a heavy-gun salvo and correct before the next loading cycle. Secondary batteries fired quickly enough to adjust while maintaining fire, and modern sensors can reduce the need for an eight-gun ranging pattern altogether. Fire-control method follows the pace of firing.