The smooth cnormal option makes the data monotonic in x and normalises the
y-values onto the range [0:1]. Points with the same x-value are replaced by
a single point containing the cumulative sum of y-values of all data points
with lower x-values (i.e. to the left of the current data point) divided by
the total sum of all y-values. This can be used to obtain a normalised
cumulative distribution function from data (useful when comparing sets of
samples with differing numbers of members).
See also
http://www.gnuplot.info/demo/smooth.htmlsmooth.dem
