To set the major and minor tick marks for the X-axis:

ch.Set 'Xtick' 12 11

The first number is the major tick interval (12 would be suitable for monthly data); the second, which may be omitted, gives the number of minor ticks in each major interval (this is ignored on 3D charts). You can also set the tick mark positions exactly with:

ch.Set 'Xtick' VEC

This trick is used in the Rainfall chart to get exact positioning of the calendar months. Note that if you use this facility, you will completely over-ride any previous settings on the axis range – the axis will be forced to span the gap from the first to the last tick mark you give.

The tick-mark interval is always a simple integer value, unless you set the axis style to ‘time’ in which case you should give a value in hours here. For axis style ‘longitude’ the tick interval is interpreted as integer degrees, for style ‘Annual’ it is years and for style ‘Monthly’ it is months.

Note that by default, barcharts place the ticks on the ends of the bars, or at the centre of each group of bars. To get the ticks placed between the bars or groups:

ch.Set 'XS'  'between'

You can place the ticks between every nth group by setting the tickmark interval:

ch.Set 'Xtick' 4  © Data in quarters

Only single integer values are allowed here.

See also ...
Using Timescale Axes