[R] scale of biplot of principal component analysis

[Moritz Lennert]

Hello,

I am trying to use the biplot function on an object (called 'acp') 
resulting from a prcomp call. However, the scale I get when calling the 
biplot function differs according to how I call:

biplot(acp) gives me a scale of -0.10 - 0.10 for the variable loadings 
and a scale of -15 - 15 for the rotated data for the first component.

However, if I look at the individual columns of the matrix, I get the 
following:

 > max(acp$rotation[,1])
[1] 0.4108393
 > min(acp$rotation[,1])
[1] -0.2117583
 > max(acp$x[,1])
[1] 5.845884
 > min(acp$x[,1])
[1] -4.932297

i.e. a scale of -0.21 - 0.41 for the loadings and -4.93 - 5.85 for the 
rotated data. These values are also used in the plot when I do:

biplot(acp$x[,1:2],acp$rotation[,1:2])

Graphically both look exactly the same, just the depicted scales are 
different.

Am I misunderstanding something, or is there something wrong with the 
default biplot(acp) call ?

Moritz