Syntax:
set zeroaxis {<linetype>} set xzeroaxis {<linetype>} set yzeroaxis {<linetype>} set x2zeroaxis {<linetype>} set y2zeroaxis {<linetype>} set nozeroaxis set noxzeroaxis etc. show zeroaxis show xzeroaxis etc.
By default, these options are off. The selected zero axis is drawn with a line of type <linetype> from the default linetype list provided by the terminal; user-defined linetypes (via the set linestyle command) are not accessible for these axes. If <linetype> is not specified, any zero axes selected will be drawn using the axis linetype (linetype 0).
set zeroaxis l is equivalent to set xzeroaxis l; set yzeroaxis l. set nozeroaxis is equivalent to set noxzeroaxis; set noyzeroaxis.