A spirit level made of high-quality, strong wood shaped as rectangle. In the center of the long side is a window with a sealed glass tube inside, containing alcohol in an amount that leaves an air bubble. When you want to make a structure precise without any slope, place the spirit level on it when the air bubble is exactly between the two lines marked on the glass tube, showing that the body being tested is straight. On one of the narrow sides of the spirit level is a round hole covered with glass and containing a tube with a bubble for measuring in a different direction. On the wooden body is a ring stamped with the inscription "BV", the name of the manufacturer Boudin Vignola, France.