The principal moments of inertia may be determined quickly and easily with the Hewlett-Packard 9100A Calculator. Accurate principal moments of inertia data is essential to determine the amount of control power required to orient a vehicle in flight and to avoid stability problems or over-design of control systems. The 9100A calculates to twelve significant digits, displays ten significant digits, and has a dynamic range of 10-98 to 1099; to achieve the accuracy needed for all calculations. The solution of principal moments of inertia usually requires the use of a large computer. The solution can now be obtained using equipment which sells for less than $5,000.