This research report documents the various types of Data Acquisition Systems in use for testing jet aircraft engines. The cost trade offs and design considerations are explored for systems which employ a digital computer as the prime recording/processing element. The digital computer has revolutionized the data acquisition field, particularly in the testing of high performance jet engines. Test data can be acquired, processed, converted to engineering units, and out via high speed line printers and cathode ray tubes (CRT's). The data acquisition system operates on-line, and interleaves the random requests for data from multiple test cells by using a specially designed software system and multi-processing capability of the high speed digital computer. All test data must be traceable to The National Bureau of Standards, which required that all calibration standards also be traceable. Primary and secondary calibration methods are discussed and examples of the mathematical processes for conversion of the raw data to meaningful results are presented. Data Acquisition Systems for jet engine testing can be logically grouped into two main categories, with the determining factor being the type of test to be conducted. Production engine testing requires rapid setup, calibration, and fast data turn around, particularly for modern automated test facilities. Development engine testing requires a large number of data channels, infrequent setup, and complete software for extensive engine performance calculations. Both types of Data Acquisition Systems have been designed and built by Pratt & Whitney Aircraft and are used as examples of the techniques described in this report.