The Hawk-Eye system is extensively used in tennis, using cameras to calculate the trajectory of the ball.

CNN: Does football need technology?

Like the Hawk-Eye system it uses a computer to send a signal to the referee's watch when a goal is scored.

CNN: Does football need technology?

The Hawk-Eye system uses strategically-placed cameras to determine the exact flight of a ball and is already used in international cricket and at grand slam tennis tournaments.

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