00:00This tiny pen is about to draw a perfect dotted line.
00:02It's called a ruling pen, and engineers used it in the 1920s to hand-draw blueprints.
00:07Inside, there's a small cam mechanism that bounces the pen tip up and down as it rolls.
00:11As it moves along the ruler, every single dash comes out identical.
00:15Today, we can do this with one click, but back then, one of these pens cost as much as an
00:19engineer's monthly salary.
Komentar