The snap line was a string coated in chalk that made a straight mark on a surface. You hooked one end to a nail and stretched the string to the other end and held it tight and pulled it up and let it go. The string snapped against the surface and left a chalk line. Blue chalk on plywood. Red chalk on concrete. The line was straight. The line was the instruction. The line said cut here or build here or stop here. The snap line was the first sentence of every construction paragraph.

The chalk box was small enough to fit in a nail apron. A reel of string inside a case filled with powdered chalk. You pulled the string out and the string dragged through the chalk and the chalk coated the string. The chalk came in colors. Blue washed off. Red did not wash off. The carpenter used blue for temporary lines and red for permanent lines. The choice of color was the choice of commitment. Blue said maybe. Red said here. The color was the confidence level of the mark.

Two men snapped a line. One man held the hook end. The other man held the box end. The men stood at opposite ends of the mark and the string stretched between them and one man lifted the string and released it. The snap was a quarter second of contact between the string and the surface. A quarter second that left a mark twenty feet long. The mark was perfectly straight because the string was pulled tight and a tight string under tension follows the shortest distance between two points. The snap line was geometry applied with a flick of the wrist.

Laser lines replaced the snap line on most jobs. A laser mounted on a tripod projects a straight line across the room. The laser line is perfectly straight. The laser line does not require two men. The laser line does not leave chalk dust on your hands. The laser line does not exist on the surface. The laser line disappears when you turn off the laser. The snap line left a mark that stayed until the rain washed it away or the concrete buried it. The snap line was evidence. The laser is a suggestion. The snap line said I was here. The laser says I am here right now but I will be gone when you look away.

See also: Chalk Reel, Mason Line