Part 1. The object of this test was to determine the suitability of the Alsop all-spark ignition device for service use on aviation engines. The Alsop device is not recommended for service use. Part 2. This portion of the document discusses the computation of distances using spherical trigonometry, including its inherent limitations. In computing distances, aeronauts and aviators on landing should always give: (a) Nearest post office. (b) County. (c) Distance and direction from the nearest town. (d) Exact measured distance and direction to the nearest railroad, road, steam, shore line, or other well-defined topographic features, which usually appear on maps.