biplot from stats: 0.8 ?

Dear forum,
I need to create biplot graphic. I took a look at the code of the biplot.default function from the stats package and I found that the arrows for the variables are multiplied by a coefficient of 0.8 before plotting:
...
if (var.axes) 
        arrows(0, 0, y[, 1L] * 0.8, y[, 2L] * 0.8, col = col[2L], 
            length = arrow.len)
...
 I have no idea why this is done. Could somebody clarify?

Thank you in advance.

Regards,
Martin