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rPHE wet-test meter is generally used for measuring large sample volumes in analysis of industrial air. The volume of a gas indicated by such a test meter under sampling conditions of temperature and pressure is not truly representative of the quantity of matter present and, for comparison with succeeding measurements, must be adjusted to an arbitrarily defined standard temperature and pressure. These standards vary among laboratories, but standard temperature is generally in the range of 20°to 30°C. and standard pressure is usually 760 mm. of mercury on a dry basis.An equation combining the laws of Charles and Boyle is generally used for this correction, but it contains four variables and may not be put too readily or compactly into table form. Barr (1) has proposed a nomogram for reducing gas volumes to normal temperature and pressure, while Patton (3) has proposed a chart for reducing volumes to standard temperature and pressure. Roof (4) has suggested a pair of nomograms for correcting volumes of gases over small ranges of temperature and over any range of pressure. The present paper describes a slide rule designed to correct gas volumes to 25°C. and 760 mm. of mercury pressure with accuracy sufficient for industrial control purposes.

The integrator method of interpreting evenness tester results to determine the degree of evenness of textile sliver, roving, and yam is rapidly growing in popularity, since it eliminates the tedious manual evaluation of evenness tester charts and furnishes percent unevenness values automatically while the specimen is under test.It is well known that evenness data furnished by the Uster Evenness Tester Chart Record and Integrator are biased and require correction [ 1. 3, 4 ~ . Correction factors, which are functions of both the instrument range and the average value, are computed from the equation Fig. 1. Slide rule. A table relating correction factors to various range and average value results is available for this purpose [ 5 ], as are a set of four tables relating apparent percent unevenness to true percent unevenness under, various range and average value conditions [ 2 ) . This letter descriltes a slide rule developed in 1952 to eliminate the need of reference tables and to reduce calculation time. The rule is applicable to the correction of average maximum percent unevenness results using the chart range method and to the calculation of average linear percent unevenness using the integrator method, The scales of the rule are shown in Figure l.The rule is constructed from a 12-in. Pickett No. 902 magnesium alloy slide rule. The white scales are first removed, using acetone and emery paper, and the blank rule is then given a layer of flat white undercoating which is baked for 24 hr at 125' C. The scales are applied manually to this surface, using black India ink, and the rule is again baked. Finally,, a coat of clear plastic is sprayed over the scales ; the plastic sold under the trademark &dquo;Kry-Ion&dquo; is satisfactory for this purpose. The scales are applied in the following manner. Scales 3 and 4 are applied first, both scales simul-1 Du Pont trademark.