This thesis presents the development and use of MECHIN, an interactive graphical preprocessor for data input to spatial mechanism analysis and synthesis codes. A goal in the development of this preprocessor is to produce a graphical data input program that is both graphics device-independent and not structured for the input of data to any particular mechanism processing program. To achieve device-independence, the proposed graphics standard PHIGS (Programmer's Hierarchical Interactive Graphics System) is used for the graphics support software. Program development strategies including screen layout and user interfaces for three-dimensional data input are discussed. The program structure is also described and presented along with a complete listing of the program code to aid in future modifications and additions. Finally, a description of the use of the program is presented along with several examples of mechanism data input for synthesis and analysis. / Master of Science