The mechanical mathematician for designing parabolic dishes

There are many ways to construct a parabolic dish. This method aims to be the simplest and most quickly adjustable one. This method does not need the input of a mathematician or any high technology people. So I call it the mechanical mathematician. I have made several paraboloids with this. I made them as proof of concept. It works but I do not know how precise it can be.

Typically I have used it to mark the correct curve on a cob mold and then used the mold as a form to construct the paraboloid. For the dual dish tracking solar accumulator, I think that the mathematician might be the ideal tool for making the approximate "Half dishes" that are needed. I think it also can be used to make good molds for home made "butterfly" parabolics.