Syntax:
set mxtics {<freq>} set mytics {<freq>} set mztics {<freq>} set mx2tics {<freq>} set my2tics {<freq>} set nomxtics etc. show mxtics etc.
<freq> is the number of sub-intervals (NOT the number of minor tics!) between major tics (ten is the default, so there are nine minor tics between major tics).
If the axis is logarithmic, the number of sub-intervals will be set to a reasonable number by default (based upon the length of a decade). This will be overridden if <freq> is given. However the usual minor tics (2, 3, ..., 8, 9 between 1 and 10, for example) are obtained by setting <freq> to 10, even though there are but nine sub-intervals.
By default, minor tics are off for linear axes and on for logarithmic axes. They inherit the settings for axis|border and {no}mirror specified for the major tics. Please see set xtics for information about these.