from the paper(o) in citation 3 from the linked wiki article(i):
> The terms "eyeballs in" "eyeballs out," and "eyeballs down" correspond
to acceleration fields AX, -Ax, and AN, respectively, where AX, -Ax,
and AN refer to the direction of acceleration forces measured in the
conventional airplane body-axis coordinate system.
> AN acceleration factor, ratio of acceleration force to weight,
positive when directed upward along spinal axis (i.e., from
seat to head )
> AX acceleration factor, ratio of acceleration force to weight_
positive when directed forward transverse to spinal axis
(i.e., from back to chest)