This circular slide rule gave approximate information on the design of deep space missions, showing the relationship among parameters such as payload weight, propellant weight, velocity, exhaust velocity, etc. It would not have been accurate enough for an engineer to use in planning a mission; they used detailed mathematical formulas, evaluated by digital computers. But the slide rule would have been very useful for managers, members of the trade press, news media, and government funding agencies, who needed to know the basics of a space mission.