How to overlay two graphs that will have different scales for the y-axes?

How to overlay two graphs that will have different scales for the y-axes?

Customer wants to overlay two graphs that will have different scales for the y-axes.  How can that be accomplished?

  Here is some sample code that demonstrates how to handle two y-axis scales:

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#Overlay graphs with different y-axes

# Creating some data to plot
x <- 1:10
y1 <- rnorm(10,10)
y2 <- rnorm(10,100)

# Pass in margins
par(mar=c(5,4,4,4)+0.1)

# Plot the first graph
plot(x,y1,type="l")

# Allow for a second plot on the graphsheet
par(new=T)

# Plot the second graph
# suppressing axes (axes=F)
# and no labels (xlab="" and ylab="")
# also changing color (col=6)
plot(x,y2,type="l",col=6,axes=F,xlab="",ylab="")

# Add an axis on the right side
axis(4)

# Add the right side y-axis label
mtext("y2",side=4,line=2.5,col=6)

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You can read more about any of the functions used above by typing a question mark followed by the function name at your S+ command prompt.  For example:

> ?axis
> ?par