Yerrorbars

The yerrorbars (or errorbars) style is only relevant to 2-d data plots. yerrorbars is like points, except that a vertical error bar is also drawn. At each point (x,y), a line is drawn from (x,y-ydelta) to (x,y+ydelta) or from (x,ylow) to (x,yhigh), depending on how many data columns are provided. A tic mark is placed at the ends of the error bar (unless set bars is used -- see set bars (p. ) for details). See also

http://www.gnuplot.info/demo/mgr.htmlerrorbar demo.