[R] Equal length axis

[Andrej Kastrin]

Dear useRs,
I am having difficulty to plot graphics with mfrow command, where both 
axis are equal length. Below is sample code, which plots rectangles 
instead of squares:

par (mfrow=c(3,3))
qqnorm(a)
qqnorm(b)
...
..

Thanks in advance for any pointers or notes.