sentences:  Each boat had to have four (or, for some canal companies - Swansea, Glamorganshire, Oxford, six) gauging plates fitted to the hull at the "corners" of the boat - bow and stern at each side - indicating a measurement point and a boat serial number.The boat was calibrated by measuring the height of the gunwales above water level at each corner with the boat unladen and then measured again when known weights had been loaded into the boat from an overhead gantry.These measurements were logged in toll-keeper's tables and copies sent to every toll office within the boat's trading range.