Chalk-Line

A chalk line: a reel of string running through a body filled with powdered chalk. Pull the line out, hold or hook both ends, lift the string and let it snap down, and it leaves a perfectly straight chalk mark however long the run - which no straight edge and no eye can match over any real distance. It is the setting-out tool of every trade that works to a line. Marking out partition and stud positions on a floor, setting tile datum lines, cutting lines on sheet and board, roofing batten and sheet lines, floor screed levels, and marking straight cuts on anything too big to reach across. Refill it with chalk powder rather than replacing it, and keep the line dry - wet string will not release its chalk.