Abstract : This document is one of a series prepared by Calspan Corporation for WPAFB WL/POTC that describes the construction and operation of the ATARR facility. This document addresses the issues surrounding the design and operation of the Data Acquisition System (DAS). The heart of the ATARR facility is the DAS. This system provides the engineers the ability to translate the voltage changes in different instruments into known, reliable engineering units. The DAS provides a context in which detailed technical questions can be answered through analysis of the basic instrumentation measurements. DAS controls all aspects of data acquisition from set-up through reduction; and, it is critical to understand the philosophy of how the system is constructed in order to best utilize its many capabilities. In a production facility, the computer system has a great deal of regimentation built into it. The test operator would not be allowed to run a test unless certain types of instruments were installed, and the number and procedures of the data reduction are limited to standard ones. Adding new reduction routines or test operations requires major changes to the computer system since there are many built-in checks to protect the test engineer from making flagrant mistakes.