Abstract
This paper describes design of a high precision water level gauge and its capability of straightness measurement of large objects. The level gauge is composed of a container of water and a float. The float has an optical linear scale to measure vertical position of the float or the water level with a resolution of 0.1 micron. Aerostatic bearings support the float vertically and enable its frictionless displacement. In the measurement, more than three level gauges are set on the object and their containers are connected to each other with tubes so that the relative heights can be measured. Then the straightness can be obtained from the relative heights among each level gauges. It was found by experiments that this method had an accuracy of better than 1 micron and was suitable for straightness measurement of large objects.
