YNozero Keyword
Used With Routines:  AXIS,  OPLOT,  PLOT
Corresponding System Variable: None.
Inhibits setting the minimum y-axis value to zero when the y data are all positive and nonzero, and no explicit minimum y value is specified (using Yrange, or !Y.Range).
By default, the y-axis spans the range of 0 to the maximum value of y, in the case of positive y data. Set bit 4 in !Y.Style to make this option the default.