relativistic velocity addition app analytics for December 23

This app shows the result for the relativistic addition of two velocities. v is the velocity of the orange rocket with respect to Earth. u is the velocity of the red rocket with respect to the orange rocket. The relativistic addition is the velocity of the red rocket with respect to the Earth. c is the speed of light. Plus button increases the velocity by 0.01c and minus button decreases the velocity by 0.01c.