Mark painted on both sides of merchant
ships to indicate the maximum point they are allowed to sink to when loaded, depending on the specific gravity
of water which varies according to season and place. This mark is accompanied by a circle bisected by a horizontal line and letters indicating the ship's registration
society. Plimsoll mark was made compulsory in 1876 in UK, and is named after Samuel Plimsoll (1824-98), a member of parliament who campaigned for better and safer work
conditions for sailors. Also called Plimsoll line.