plot(c(0,90),c(0,30),type="n",xlab="", ylab="")
abline(v=seq(0,90,5), h=seq(0,30,1), col="blue",lty=3)
abline(h=0, v=0, col="brown")
f <- function(x) (0.26+runif(1)*0.04)*x; g <- function(x) floor(x*3-1); h <- function(x) floor(x*3-1)
a <- c(22+g(runif(1)),40+g(runif(1)),57+g(runif(1)),79+g(runif(1)))
b <- floor(c(f(a[1])+g(runif(1)),f(a[2])+g(runif(1)),f(57)+g(runif(1)),f(a[4])+g(runif(1))))
x <- array(dim=c(4,2)); y <- array(dim=c(4,2))
x[1,1] <- a[1]-3; x[1,2] <- a[1]+3
y[1,1] <- b[1]-1.5; y[1,2] <- b[1]+1.5
x[2,1] <- a[2]-3; x[2,2] <- a[2]+3
y[2,1] <- b[2]-1.5; y[2,2] <- b[2]+1.5
x[3,1] <- a[3]-3; x[3,2] <- a[3]+3
y[3,1] <- b[3]-2; y[3,2] <- b[3]+2
x[4,1] <- a[4]-3; x[4,2] <- a[4]+3
y[4,1] <- b[4]-2; y[4,2] <- b[4]+2
i <- 1:4; rect(x[i,1],y[i,1],x[i,2],y[i,2],border="red")
pm <- max(y[i,1]/x[i,2]); pM <- min(y[i,2]/x[i,1])
abline(0,pm); abline(0,pM)
# pm; pM