One of the easiest projectors is the model E-5 and comprises just the basic functions with very simple operation. The star ball is 30 cm in diameter and harbours 750 stars down to the 3rd magnitude plus some selected fainter stars. The planets are enclosed in the cylindrical cage that balances the weight of the ball. The annual rotation proceeds in 4 minutes per year. The projector is meant for a 5 m dome. Goto produced this model for more than three decades with only slight variations. About 300 units were sold worldwide.