Document Type: Technical Research Report Authority: Government Military (authoritative reference) Document Number: Air Service Information Circular (Aviation) Vol. V, No. 439 (dated May 1, 1923), based on McCook Field Report Serial No. 2089 (dated November 14, 1921).

Scope: Report prepared by W. F. Gerhardt of the Airplane Section, Engineering Division, Air Service, McCook Field.

Contents: See title. From page (1) " Doctor de Bothezat designed his "pressure step" barograph for the general purpose of studying this new type of instrument and with the specific idea of developing a more sensitive instrument for his method of flight testing. The low sensitivity of the ordinary barograph, especially when adjusted to high altitude ranges, brought about the consideration of a method of increasing the accuracy of a new type of instrument.

Essentially this instrument consists of a large silk bellows connected to an expansion tank in which the presence is automatically brought to atmospheric at the limit of expansion by a special valve and system of electrical contacts. The instrument is designed to be independent of the temperature."

From page (3): "GENERAL OBSERVATIONS. In conclusion are added several deductions made from the short experience with the instrument: (1) This instrument was only built to illustrate the principle of operation. In consequence it was built large and heavier than a practical usable instrument would be. Although a number of flights were made with it, it was found quite awkward to handle in even a two-seater plane."