Grasshopper Gold

Hello sir, I want to create a 3 point arc using ‘gg_gumball’

But i don’t know how to use that component,
(My task is to make a curved pipe in 3d view, but the length of pipe will not same all time, so i want a gumball like 'rope builder ’ in grasshopper gold plugin ’ two ui points that can control length of curve or subcurve.

I know it’s not very clear by words what I’m trying to do, without a 3D presentation.

(But I’ll attach that soon)

Good luck with that.