Surface level

Using the level

 * 1) Look at the two tubes in the level. The tubes will be filled with a fluid and there will be a bubble floating in the fluid. Each tube will have two lines on them near the center of the tubes. There is a horizontal tube which is parallel to the body of the level and a vertical tube which is perpendicular to the body of the level.
 * 2) Place the level on a horizontal surface so that the horizontal tube is parallel to the surface.
 * 3) Examine the horizontal tube. If the bubble is in the center of the tube between the two lines the surface is flat. If the bubble is more towards one end or the other the surface is slanted. The farther the bubble is on either side the more slanted the surface.
 * 4) Put the level against a vertical surface so that the vertical tube is perpendicular to the surface.
 * 5) Check out the vertical tube. If the bubble is in the center of the tube between the two lines the surface is flat. If the bubble is more towards one end or the other the surface is slanted. The farther the bubble is on either side the more slanted the surface.
 * 6) Adjust the surface as necessary while holding the level against it. When the bubble centers between the two lines the surface is perfectly horizontal or vertical.