Setting manual tics

Sometimes gnuplot's various automatic tic generation routines are not flexible enough and you need to take complete control of the position of every tic mark, or you need to place custom labels on the tics rather than rely on the automatically generated numerical labels provided by the program. gnuplot is extremely flexible in this regard; the following figure illustrates our first example of manual tic placement:

Notice the tic labels and positions along the x-axis. The tics are aligned with the peaks and zero crossings of the sine wave, and are labeled using pi rather than an approximate decimal. This is more meaningful mathematically and is the natural way to label the axis when plotting this circular function. gnuplot's automatically chosen tic positions and numerical labels would be placed at the positions 1, 2, 3, and so on. These tic positions would have no particular relation to the function we are plotting. In order to get the result in the figure, we need to...