[R] normalized frequency histogram

[Jim McLoughlin]

Hi folks

I'm trying to plot a normalized frequency histogram of some data.  
After checking the docs, it seems there is no built in feature for this.

from the definition for normalized frequency, I need to divide the 
relative frequency by the size of the intervals being used.

So I could divide the series by this interval length, and then plot the 
relative frequency.

The problem is determining the interval length that will be used in 
advance.  I'm supposed to manually pick the # of intervals between 20 
and 40 (not use sturges).  However, when I try different values for the 
nbreaks parameters, incrementing from 20 - 40, the histogram only 
changes at a couple of points on that interval.

Anyone have any suggestions as to how I should create this plot?  Or an 
explanation as to why my nbreaks parameter does not seem to force the 
number of intervals, but rather suggests a ballpark to be in?

thanks

Jim M