PHASER is a sophisticated program for IBM personal computers, developed at Brown University by the author and some of his students, which enables users to experiment with differential and difference equations and dynamical systems in an interactive environment using graphics. This book begins with a brief discussion of the geometric interpretation of differential equations and numerical methods, and proceeds to guide the student through the use of the program. To run PHASER, you need an IBM PC, XT, AT, or PS/2 with an IBM Color Graphics Board (CGB), Enhanced Graphics Adapter (EGA), or Video Graphics Adapter (VGA). A math coprocessor is supported; however, one is not required for PHASER to run on the above hardware.