Visualization of Ypsilon illusion: As in all tumbling blocks, the basic blocks (step 1) are made of light, medium and dark values. The shading creates the illusion of a three dimensional cube (we used 25%, 50% and 80% values). We took individual blocks and stacked them, one at a time, to form the Y shape (step 4). If you count the number of light, medium and dark diamonds in step 4 you'll see that there are 3 of each. The pattern is then formed by staggering the Y shapes, as shown (step 5).