Sunspeed device shows that shadow should advance trigonometrically with constant angular speed passing a new ring each 10 minutes and the rising shadow should remain aligned to the linear grove once set. The initial position has to be the one without the shadow at all. The device has to prove or disprove astronomical global model of Earth in every single classroom in the world!
This didactical toy is copyrighted.
It is 3D: click it with mice to rotate
and roll the middle button to zoom.
Flat PDF version is available as sunspeedc.pdf.