watch mouse

Using the current mouse x coordinate as a watch target generates a label that moves along the line of the plot tracking the horizontal position of the mouse. This allows simultaneous readout of the y values of multiple plot lines in the same graph. The appearance of the point indicating the current position and of the label can be modified by set style watchpoint and set style textbox

Example:

     set style watchpoint labels point pt 6 ps 2 boxstyle 1
     set style textbox 1 lw 0.5 opaque
     plot for [i=1:N] "file.dat" using 1:(column(i)) watch mouse