For any point P(x1, y1) on $x^2$/$a^2$ - $y^2$/$b^2$ = 1: SP = |ex1 - a| and SP' = |ex1 + a|. For points on the right branch (x1 > 0): SP = ex1 - a, SP' = ex1 + a. So SP' - SP = 2a. For the left branch: SP - SP' = 2a. The latus rectum (minimum focal chord) has length 2$b^2$/a. The harmonic mean of the segments of a focal chord equals the semi-latus rectum $b^2$/a.