The JLF-SP-R spring is taken from the official Sanwa kit to optimize the JLF series joysticks.
It allows you to adjust the stiffness of the rod, both at the start and at the end of the race (see detail in the diagram).
The table shows the forces exerted by the different springs at two times of the stroke of the rod.
For the red spring, the tension is 2 times that of the original spring, when the handle is in position 1.
And, the tension is 2 times that of the original spring when the handle is in position 2.