This is it. It shows a clock as a beam of light bouncing between two mirrors. The beam in the moving vehicle has to move a further distance relative to the stationary clock, so the ticks slower in the moving vehicle.
CLICKY Hit play on the first animation
__________________
Heritage EL Fairmont Ghia - Turbo DOHC Build
Petroleum FG MKII XR6 Turbo - 350rwkw
Magnetic 2017 Mustang GT - 300rwkw