x <- as.numeric(time(nhtemp))
y <- as.numeric(nhtemp)
n <- length(x)
mean <- mean(y)



x <- as.numeric(time(nhtemp))
y <- as.numeric(nhtemp)
n <- length(x)
mean <- mean(y)

par(mfrow=c(2,2), mar=c(3, 3, 1, 1))
plot(x, y, type="n", axes=FALSE, ann=FALSE)
polygon(c(x[1], x, x[n]), c(min(y), y, min(y)), 
        col="gray", border=NA)

box(col="gray")
plot(x, y, type="n", axes=FALSE, ann=FALSE)
polygon(c(x[1], x, x[n]), c(min(y), y, min(y)), 
        col="gray", border=NA)

usr <- par("usr")
rect(usr[1], usr[3], usr[2], mean, col="white", border=NA)

box(col="gray")
plot(x, y, type="n", axes=FALSE, ann=FALSE)
polygon(c(x[1], x, x[n]), c(min(y), y, min(y)), 
        col="gray", border=NA)

usr <- par("usr")
rect(usr[1], usr[3], usr[2], mean, col="white", border=NA)

lines(x, y)

box(col="gray")
plot(x, y, type="n", axes=FALSE, ann=FALSE)
polygon(c(x[1], x, x[n]), c(min(y), y, min(y)), 
        col="gray", border=NA)

usr <- par("usr")
rect(usr[1], usr[3], usr[2], mean, col="white", border=NA)

lines(x, y)

abline (h=mean, col="gray")
box()
axis(1)
axis(2)