Hey Uwe! This is super cool and I’m really excited about it. A classmate and I are going to use it to possibly build a museum exhibit in which participants roll a skateboard around on a ramp to learn about (and feel) velocity, acceleration, minima and maxima and horizontal points of inflection. Thanks!
(Teresa, the same thing happened to me and it turns out I had calibrated wrong. Check your calibration details, and if it looks like an hourglass, then you accidentally clicked the wrong crosshair at some point in the calibration.)