The Acceleration Performance Instrument was developed to reduce the manpower and equipment required for vehicle performance testing. Using only a single person and test vehicle, data may be obtained in five operating modes.The instrument prints time-to-speed and time-to-distance information on paper tape during vehicle acceleration and coastdown. Acceleration testing may utilize a standing or moving start at any speed up to 99 mph. Vehicle coastdown data may be obtained between any two speeds and is useful for determining aerodynamic drag and rolling resistance. Special modes provide Federal consumer passing information without the use of additional personnel or vehicles. The instrument requires the addition of a 5th wheel and an AC power inverter for operation.THE ACCELERATION PERFORMANCE INSTRUMENT was developed to meet the demands of increased performance measuring capability using reduced manpower and vehicle time. Previously, performance tests had been run using various stopwatch and 5th wheel speedometer schemes or 5th wheel and analog strip chart recorder methods. These methods, while adequate, were time-consuming, prone to human error, and in many cases required two or more people for execution. An ever increasing number of performance tests, plus the necessity of measuring new vehicle performance parameters such as coastdown and Federal consumer passing information, precipitated the development of a new performance measuring instrument. This instrument needed to be automatic where possible, operable by one person, and produce accurate printed data.The Acceleration Performance Instrument (API) fulfills the above requirements and provides additional features such as driver aids and test data summaries. A description of the various operating modes and data provided in each mode is given in the Instrument Capability section. All these capabilities are available in a small, easy to operate, easy to install package. The API is shown in Figure 1 and a typical installation in Figure 2. The primary transducer for the API is a 5th wheel equipped with a tach generator for analog speed output and a one-pulse-per-foot distance output. In addition to the API and 5th wheel, an AC power inverter is required to power the instrument's digital printer.The accuracy of the instrument is listed in Appendix 2. A block diagram, showing the API's internal microcomputer and related hardware, is shown in Figure 3. A more complete hardware description is located in Appendix 3.