you need to choose the interval or bin width.
What is the best bin width?
Probability of a height being in a particular interval
= number in column/ total number
= area of column/total area of columns
= N(h)dh / SN(h)dh
The frequency distribution is converted to a probability distribution
dividing the number per interval by the total number in all intervals.
Note: total probability = SP(h)dh = 1