but machinbird I am shure, there is a smal mistake in the drawing both springs will work in hook´s law, but the bigger(purple) spring IMO is a few mm shorter than shown, there is more space on the yellow side..... so first you press the weaker green spring and later you have to ad the hooks force of green and purple
Grity, it is quite possible that you are correct and there is actually some spring freeplay that is not shown in the drawing. It is also possible to make a non-linear compression spring by wrapping the spring in such a way that the adjacent loops make contact in only a portion of the spring and thus effectively shorten the active portion of the spring. The guys who make springs can do it very consistently, even with 50 year old equipment.