A hydrostatic level for elevation surveying has been developed which indicates differences in elevation by measuring the head of a column of water. It is essentially a differential pressure gauge connected by a length of water-filled plastic tubing to a water reservoir. The instrument is described and the results of a field test on 73 miles of traverse are given. A probable error of about 6 cm and a maximum error of 33 cm were found for closed loops of 3 to 5 miles after proration of closure errors. On unsupported traverses of 3 to 5 miles, application of a temperature correction appeared desirable and resulted in a probable error of about 10 cm and a maximum error of 52 cm. The range of the instrument is from minus to plus 10 meters and the least count is 2 cm. It is read to the nearest centimeter.

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