09:05, the board, before the axes
The vial is not straight. It is an arc of a large circle, and the bubble rests at the highest point of the arc, because that is where the liquid’s weight puts it: an equilibrium you can watch arrive. Tilt the rule through an angle θ and the bubble runs s = Rθ along the glass, so the sensitivity of a level is nothing but a radius. This one is ground to R = 2 m: a slope of one millimetre in a metre moves the bubble two millimetres.
Objects · Board straightedge with a spirit level
Level Rule
CHF 85 working price
For an x-axis that is actually horizontal, and a poster that hangs straight.
A straightedge for the board, in pear wood with brass ends and one glass vial let into its face. No graduations: on a blackboard the unit is whatever you say it is.
A study: nothing can be ordered yet. The photograph is a generated image, not a picture of a made piece or of a real person.
- Pear wood, oiled, with brass end caps: 500 × 40 × 12 mm, about 230 g
- One glass vial ground to a radius of 2 m, let into the face behind a brass window, so it reads with the rule flat against a board
- The spirit is tinted vermilion; the bubble is the gap in it. Two fine lines engraved on the glass mark the middle
- No other marks anywhere, and no numerals; a turned knob to hold it by, and a hole at one end for the ledge hook
- Numbered on one brass cap. The bubble is the only part that moves
