I'm using the chain/strap/linkage as the unchanged length. It isn't factored in being that it's length remains constant. Yet it is what transfers work from the footboard to the cam. This is the length I'm referring to.The effective length is constantly changing, so it's called effective. The physical (material) length does not change.
I'm not saying you are measuring wrong. I'm saying the footboard doesn't travel vertically, it travels in an arc. So if someone were to put a tape measure on the floor and measure the up and down, it isn't the same distance as the length of arc where the linkage and footboard meet.Do you know what I'm measuring? How can you say this is the wrong measurement? And what exactly do you want to measure?
I think we are on the same page, just words getting in the way. Perhaps I'll draw a diagram.