Histogram chart - What do the y-axis numbers mean?

["Marlon Nelson" <marlon nelson gmail com>]

I originally thought this was a bug and was about 30 seconds from
submitting one to bugzilla when I began to suspect the problem is with
my understanding of what a histogram is.

With the data listed below (frequency of daily returns of Merrill
Lynch stock over the last 10 years), I created a histogram chart.  The
highest point on the chart reaches 50,000.  I was expecting 1011.

Reading a bit from wikipedia, I see what I was actually expecting to
see is a bar chart.

But given a histogram chart of this data, what do the y-axis numbers mean?

Bin	Frequency
-15%	1
-13%	1
-11%	4
-9%	6
-7%	13
-5%	53
-3%	167
-1%	510
1%	1011
3%	489
5%	156
7%	57
9%	26
11%	6
13%	4
15%	3
17%	2

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-eom-