Tool tips on tapping automatic levels and the definition of a surveying system.
A: Automatic levels work on the principle of a movable optical component, usually a prism, or a mirror that is suspended and responds to the pull of gravity, orienting itself to assure a horizontal line of sight through the instrument. When automatic levels were first introduced and before the technology was mature, the development of almost frictionless suspension systems for these optical components was ongoing. In testing, it was discovered that not quite horizontal lines of sight were occasionally established due to friction, preventing the optical components from coming to rest where they should. Many surveyors developed the habit of tapping the instrument with a finger just prior to taking a reading. This was to cause the optical component to vibrate slightly, and if it hadn't been in the correct position, to help it get there. Today's levels have much improved suspension systems and rarely, if ever, need such a helping tap. If you do choose to tap the instrument, tap it lightly enough to be sure the reading isn't disturbed. By checking the rod reading before and after tapping you will develop a feel for applying the right amount of force without causing error. Even if the prism "sticks" it shouldn't be happening with every reading. If you observe such a condition, discontinue use immediately and take it to a qualified repair shop for evaluation and servicing.
Q: Many people make reference to a surveying system. Why do they use this term instead of "instrument"?