Mass increment sign change at the moving of three horizontal material points along straight directing lines

The Material Science task which has the geometrical solution as the construction of three hyperbolic paraboloids with horizontal generating lines given by two of three initial straight lines is considered in the article. As it is shown three straight conoids with a common vertical directing line and horizontal generating lines are connected with this construction. Moreover every conoid is intersected with one of hyperbolic paraboloids along its criminant.