x <- 1:30 
y <- seq(1, 300, 10) + rnorm(30)

y[5] <- y[5] + 10
y[10] <- y[10] + 5
y[25] <- y[25] - 10
fit <- lm(y ~ x)
plot(fit)

y[5] <- y[5] + 15
y[10] <- y[10] + 20
y[25] <- y[25] - 15
fit <- lm(y ~ x)
plot(fit)

y[5] <- y[5] + 30
y[10] <- y[10] + 40
y[25] <- y[25] - 30
fit <- lm(y ~ x)
plot(fit)

y[5] <- y[5] + 60
y[10] <- y[10] + 80
y[25] <- y[25] - 70
fit <- lm(y ~ x)
plot(fit)

y[5] <- y[5] + 100
y[10] <- y[10] + 120
y[25] <- y[25] - 150
fit <- lm(y ~ x)
plot(fit)

x <- 1:100
y <- seq(1,300,10) + rnorm(100)

y[5] <- y[5] + 20
y[10] <- y[10] + 10
y[25] <- y[25] - 20
fit <- lm(y ~ x)
plot(fit,col=rainbow(100))