Combination of two pantograph mechanisms.
Yellow and orange bars create a rhombus.
Center distances from middle hole to end holes of yellow bar are equal.
Pink, violet, grey and green bars create a rhombus.
Center distances from middle hole to end holes of pink or green bar are equal.
The mechanism ensures: OA + OB = OC
Move slider A to enter value X
Move slider B to enter value Y
Slider C shows S = X + Y
The video shows the operation 1 + 3 = 4 and the return to initial position.