[Dave Scheck]

You may want to check out the class that's posted here.

To directly answer your question though, it's a combination of axes 5 (x) and 6 (y).

if (x < -0.5 && y < -0.5)
        return kUpLeft;
    if (x < -0.5 && y > 0.5)
        return kDownLeft;
    if (x > 0.5 && y > 0.5)
        return kDownRight;
    if (x > 0.5 && y < -0.5)
        return kUpRight;
    if (y < -0.5)
        return kUp;
    if (x < -0.5)
        return kLeft;
    if (y > 0.5)
        return kDown;
    if (x > 0.5)
        return kRight;

    return kCenter;