The MajTickLen value should be given as a fraction of the minimum dimension of the plotting area. Negative values cause major tick marks to be placed on the outside of the corresponding grid line or axis (but subject to any clipping imposed by PGPLOT ), while positive values cause them to be placed on the inside.
The default behaviour depends on whether a co-ordinate grid is drawn inside the plotting area (see the Grid attribute). If so, the default MajTickLen value is zero (so that major ticks are not drawn), otherwise the default is .
KAPPA --- Kernel Application Package