I wanted to surface this item as a separate topic, even through it has been covered in the general introduction to the Shotoism Rule.
Itosu's pinan/heian katas did not walk an H-shaped pattern. The "wings" of the pattern were angled at 45 degrees, making the embusen look like a two-headed arrow. We still see hints of that heian yondan, and in the repeated clusters of four shuto-ukes that we see in various katas.
Funakoshi flattened out the wings of the heians to make the now-familiar H-shaped pattern on the floor.
The great significance of this change is that it identifies the karate styles that got their heians from Shotokan. When you see the H on the floor, you know the style had a Shotokan ancestor. Some styles readily admit this (Wado Ryu) but others vehemently deny it (Taekwondo).
Also, it is occasionally important to keep in mind that the turns in the katas used to be shallower. This makes it much easier to see how to use them as throws.