The stationary objects to be measured are machine housings, foundations, structures, and machine slides or other parts that do not rotate. The two reasons for making such measurements are to orient the machines or structures to be level with the earth, or to align one relative to another. These measurements are done during initial construction and installation. The instruments are generally sensitive enough to measure changes over time, or thermal growth changes. These latter will be called dynamic movements, because they are usually reversible when the machine is stopped. Being dynamic, they could be considered as a low-frequency oscillation, with a period equal to the start/stop cycle. These dynamic movements could be mechanical or thermal in origin.

The general method of detecting these "movements" of stationary objects is to establish a reference point that does not move. The distance of two or more points on the object from the reference is measured as a baseline. Then these distances are re-measured at later times after some changes have occurred. The objective is to determine the direction and amount of these relative changes. The available methods are:

• Mechanical Distance Measurements

• Optical Angular Tools

• Electronic Transducers

An assumption with all of these methods, worth repeating, is that the reference points are absolutely stationary. An additional assumption with only two points on the machine is that the machine is a rigid body and does not flex. If the degree of flexure is desired to be known, more than two target...