(This article was first published on

**"R-bloggers" via Tal Galili in Google Reader**, and kindly contributed to R-bloggers)I’ve been asked how to do this several times, so I thought it might help to put an example online.

x <- 1:5 y1 <- rnorm(5) y2 <- rnorm(5,20) par(mar=c(5,4,4,5)+.1) plot(x,y1,type="l",col="red") par(new=TRUE) plot(x, y2,,type="l",col="blue",xaxt="n",yaxt="n",xlab="",ylab="") axis(4) mtext("y2",side=4,line=3) legend("topleft",col=c("red","blue"),lty=1,legend=c("y1","y2"))

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