XZERO

Syntax: SET XZERO n
GET XZERO { n }
Default: XZERO = 0

XZERO controls whether or not to force zero to be displayed on the x-axis.

XZERO = 0 do not force zero to be displayed on the x-axis
XZERO ≠ 0 if XMIN ≥ 0 then set XMIN to zero, or,
if XMAX ≤ 0, then set XMAX to zero.