HOLE MEASURER

Disclosed are methods and apparatus for rapidly, accurately and inexpensively measuring either the length, or, alternatively, both the length and diameter, of a hole in a substrate. According to this invention a first electromagnetic beam is positioned upon the hole at a first angle with regard to the axis of the hole and a second electromagnetic beam is positioned upon the hole at a second angle with regard to the axis of the hole. The quantity of energy in the portion of each of the beams that pass through the hole is sensed and the ratio of the sensed quanties of energy is determined. The ratio of the length and diameter of the hole are mathematically correlated in terms of the relationship between the first and second angles and the ratio of the sensed quanties of energy. The mathematical correlation is then solved for the ratio of the length and diameter. The length of the hole is then determined by multiplying the ratio of the length and diameter by a value reflective of the diameter of the hole, which can be either a nominal value or a value determined by solving a mathematical correlation of the diameter of the hole in terms of the energy in the portion of the first light beam passing through the hole.