A combination of old and new. The "viewer" is as old as the ancient Greeks. Hold the John Pike Wonderful Perspective Machine at arms length, scan around and pick your composition. The "grid" on the blue plastic has 3 lines vertically and 3 lines horizontally, simply mark lightly the same lines on your paper or canvas, which has approximately the same proportions.
There is a magnetic inner frame with spring steel cross bars that go in any direction you place them. All you have to do is line up the bars with your various angles, note where they cross the squares on the "viewer", then mark the same on your squared-off canvas or paper.
An added touch is the blue tint which neutralizes color, so you may more clearly see the true values.The John Pike Wonderful Perspective Machine comes complete with a soft carrying case.