The smooth fnormal option work just like the frequency option, but produces
a normalized histogram. It makes the data monotonic in x and normalises the
y-values so they all sum to 1. Points with the same x-value are replaced by a
single point containing the sumed y-values. To plot a histogram of the number
of data values in equal size bins, set the y-value to 1.0 so that the sum is a
count of occurrences in that bin. This is done implicitly if only a single
column is provided.
See also
http://www.gnuplot.info/demo/smooth.htmlsmooth.dem
