Long Magic Mirrors 4,5x11,5 inch (folding), Marti Michell
With this tool by Marti Michell, multiple reflections create the illusion of an entire block. In fact, it works like a series of mirrors. The fabrics in the diagram are reflected in such a way as to show what the block would look like if it were made by repeating the patchwork section in the same colour.
The Magic Mirror can also be used to preview what the block would look like when made by repeating a specific fabric design (see image of medallion fabric).