eqscplot {MASS}  R Documentation 
Version of a scatterplot with scales chosen to be equal on both axes, that is 1cm represents the same units on each
eqscplot(x, y, ratio = 1, tol = 0.04, uin, ...)
x 
vector of x values, or a 2column matrix, or a list with components
x and y

y 
vector of y values 
ratio 
desired ratio of units on the axes. Units on the y axis are drawn at
ratio times the size of units on the x axis. Ignored if uin is
specified and of length 2.

tol 
proportion of white space at the margins of plot 
uin 
desired values for the unitsperinch parameter. If of length 1, the desired units per inch on the x axis. 
... 
further arguments for plot and graphical parameters. Note that
par(xaxs="i", yaxs="i") is enforced, and xlim and
ylim will be adjusted accordingly.

Limits for the x and y axes are chosen so that they include the
data. One of the sets of limits is then stretched from the midpoint to
make the units in the ratio given by ratio
. Finally both are
stretched by 1 + tol
to move points away from the axes, and the
points plotted.
invisibly, the values of uin
used for the plot.
performs the plot.
Arguments ratio
and uin
were suggested by Bill Dunlap.
Venables, W. N. and Ripley, B. D. (2002) Modern Applied Statistics with S. Fourth edition. Springer.