In the default situation, GNUPLOT expects to see three or four numbers on each line of the data file, either (x, y, ydelta) or (x, y, ylow, yhigh). The x coordinate must be specified. The order of the numbers must be exactly as given above. Data files in this format can easily be plotted with error bars:
plot "data.dat" with errorbars
The error bar is a vertical line plotted from (x, ylow) to (x, yhigh). If ydelta is specified instead of ylow and yhigh, ylow=y-ydelta and yhigh=y+ydelta are derived. If there are only two numbers on the line, yhigh and ylow are both set to y. To get lines plotted between the data points, plot the data file twice, once with errorbars and once with lines.
If y autoscaling is on, the y range will be adjusted to fit the error bars.
The using option may be used to specify how columns of the data file are to be assigned to x, y, ydelta, ylow, and yhigh. The x column must be provided and both the x and y columns must appear before the errorbar columns. If three column numbers are given, they are x, y, and ydelta. If four columns are given, they are x, y, ylow, and yhigh.
Examples:
plot "data.dat" using 1:2:3:4 with errorbars
plot "data.dat" using 3:2:6 with errorbars
plot "data.dat" using 3:4:8:7 with errorbars
The first example reads, x, y, ylow, and yhigh, from columns 1, 2, 3, and 4. This is equivalent to the default. The second example reads x from the third column, y from second and ydelta from the sixth column. The third example reads x from the third column, y from the fourth, ylow from the eighth, and yhigh from seventh columns.
See also plot using and plot style.