, the second is orthogonal to
the first and to the cartesian 
, and the third is orthogonal to the first
two.
x,y,z specify the unnormalised direction cosines of one of the three
axes defining the grid. Up to three AXIS commands can be given, but
none is required. Axes need not be orthogonal.
By default, the first axis is the cartesian , the second is orthogonal to
the first and to the cartesian , and the third is orthogonal to the first
two.