Safety roundtable on runway incursion prevention

An electrical system for use in optical densitometry. The system includes a plurality of separately operable electrical circuits contained in a single unit, and each circuit is adapted to produce response characteristics in a single voltmeter or other associated readable instrument which characterize one selected property or characteristic of the specimen being analyzed. In use, with the electrical system operatively associated with a photometer and a voltmeter or the like, the user, by merely manipulating a single control, may select a circuit which will produce a readable signal indicative of the characteristic he wishes to measure, and such indication or measurement may then be read directly from the voltmeter, for example, while moving the switch to other positions will select other circuits and cause the voltmeter reading to indicate measurements of other characteristics of the same sample. All these operations may be carried out without the necessity of changing the sample, the photometer, the connections thereto, or the character of the voltmeter or other instrument providing the reading. The characteristics typically able to be read include (a) percent dot area of a half tone specimen, (b) the percent of light transmitted through or reflected from the specimen, and (c) the optical density of the specimen. The electrical circuits are arranged so that the signal furnished to the meter for indicating percent dot area is inversely proportional to the strength of the incident light, so that for indicating light transmission percentage, the signal furnished to the meter is directly proportional to the strength of the incident light, and so that for indicating optical density, the signal furnished to the meter is inversely proportional to the logarithm of the strength of the incident light.