All you need for the next recipe is to type it at the R prompt as we will use some base library functions to define a new error bar function. You can also save the recipe's code as a script so that you can use it again later on.

Let's draw vertical error bars with 5 percent errors on our cars' scatter plot using the arrows() function:

plot(mpg~disp,data=mtcars)

arrows(x0=mtcars$disp,
y0=mtcars$mpg*0.95,
x1=mtcars$disp,
y1=mtcars$mpg*1.05,
angle=90,
code=3,
length=0.04,
lwd=0.4)

To add horizontal error bars (also 5 percent in both directions) to the same graph, run the following code after creating the preceding graph:

arrows(x0=mtcars$disp*0.95,
y0=mtcars$mpg,
x1=mtcars$disp*1.05,
y1=mtcars...