Surveying, if you check the dictionary, sounds like a discouragingly difficult procedure. In practical language, however, it simply means accurate measurement. To the contracor, its a form of insurance against a foundation winding up two inches over somebody else's property line. There are two basic types of builders' instruments- the optical level which has its telescope fixedin a horizontal position, and the transit-level, which runs not only sideways, but also up and down. This enables you to determine whether a wall is perfectly plumb. The transit-level also allows you to run straight lines and to measure vertical angles. The optical level consists of a telescope, leveling screws, the vial or "bubble" and a 360 degree scale. Cross hairs within the telescope enable you to center your target. Before you line up the telescope, though, you must first level the instrument by means of the leveling vial and leveling screws. By turning screws A and B, and watching the bubble carefully, the instrument can be leveled on the A/B axis. The telescope is then given a quarter turn to the C/D axis and leveled again. After rechecking, the telescope can then be turned around the complete 360 degree circle and found to be perfectly level in every direction. For an example of how the optical level works, let's assume that you want to establish the foundation corners of a house: (1) you start with an empty lot. (2) You intend to put this rectangular shaped house on it, and you need to square off the four corners accurately. (3) Let's assume we have established the front of the building line- start by setting up our instrument at A, leveling it up and pointing toward B. Then we set the circle or pointer to 0 degrees. (4) Now, we swing our telescope exactly 90 degrees, which establishes the direction of point C. We measure off the correct footage from A to C with a tape and drive in a stake at C. (5) Now, we move our instrument to point C. We sight back on A and set the horizontal circle at zero. (6) Next, we swing our level 90 degrees and establish point D. Tape the length and drive in a stake at D. (7) We have now established our foundation corners. A perfect rectangle has been established in a matter of minutes.