H = Go Home.
S = Skip past the navigation and go straight to the content.
0 = Go to the accesskey definitions page / Accessibility page.

1 to 0 (e.g. 1, 2, 3 8, 9, 0) = The main navigation items, in our case:
1 = About Us
2 = Market Rules
3 = About The Market
4 = Market Data
5 = EMC Services