R - plot with two different y-axes on top of each other

1 two plots on top of each other

• first create to vectors of y-values
  
• then set the margins appropriately
  
• then we plot the first series of y-values and plot the axis title
  

y.plot1 <- sort(runif(10))
y.plot2 <- runif(10)*5
par(mar=c(5,6,2,4))
plot(y.plot1,lwd = 4,ann=F,las=2,type="l")
mtext("y.plot1",side = 2,line=3.5)

• now we set the graphics parameter new to TRUE ; this causes R not to clean the plot before the next high level graphic command is executed
  
• then we plot the second plot without annotations (because we want the axis on the right side, which would be plotted on the left side by default)
  
• then we plot the y-axis on the right side of the plot (the four in axis(4, ...) indicates the side) and add the annotations
  

y.plot1 <- sort(runif(10))
par(new=T)
plot(y.plot2,ann=F,axes = F,col="red",type="l",lwd = 4)
axis(4,col="red",col.ticks = "red",lwd=3,at=0:4)
mtext("y.plot2",side = 4,line=3,col="red")