Set the motor's starting position to "Started"

If motor's position is 0 that means it's one rotation, so add 360 to "Rotations"

Set it to forever, when botten is pressed.

Set "Ended" to the new position of motor + the rotation count.

Set "Cm" to 17.5 (Small wheel's circumference) * "Ended"- "Started"  divided by 360 (for the rotation count) = distance traveled

Math note:
17.5 * [ ( "Ended" + "Started" ) / 360] = distance traveled

Broadcast a message.

Repeat 2 times (text) so you won't miss the it.
Write "Cm" on screen.

When left button pressed, reset all variables to 0.