If the preload and the decrement item are not considered, the force by the spring appears as below Figure 1. In this case, the force is 0 when the value of distance between two markers is same with the value of free length.
•When the value of distance between two markers is smaller than the value of free length, it generates the plus force considered the compressed state.
•When the value of distance between two markers is bigger than the value of free length, it generates the minus force considered the tensile state.
Figure 1 Force by the Spring
Figure 2 Force as the Equilibrium State
Figure 3 Decrease and Increase Free Length