Two ends of the cable are fixed to the base.
Move the green slider to enter value a.
Move the blue slider to enter value b.
The violet cursor (fixed to the cable) gives value 2(a+b).
The video shows the operation 2(0.5 + 1) = 3 and the return to initial position.
For getting value (a+b) to connect the violet cursor to further mechanism such as to the pink slider in video “Cable drive 3” of this channel.