The digital computer has greatly enhanced the ability to analyze accurately the performance of hydrostatic and hydromechanical transmissions. The requirements for developing a computer program for analyzing the transmission's performance were to: 1. Describe the transmission's performance data in a manner readily usable by the digital computer. 2. Obtain accurate data from the hydraulic components. 3. Prepare a program which is capable of analyzing the transmission's performance at any combination of operating conditions throughout the operating spectrum of the transmission. 4. Present the output data in a form readily usable by design and application engineers.This paper describes how the above program was developed for analyzing both the transmission's performance and performance of vehicles using the transmission.