Mean vs average

Question

Hi,
The "mean" tool in help is described as:
"mean is the mean, or average, of the values in the input sequence X."
However, when feeding a very large array of single precision numbers into this function, I get a different result than when I take the same array, total up the values in the for loop, and divide by number of samples. 
Opening up the "mean" tool vi, it is a dll call which I can't tell what is being done under the hood.
The size of the array has 3,554,361 elements, the source of which is a tdms file where we've gather current data over a period of roughly 49 hours.  There was a enough of an error where a noticable difference in our mAh calculation was apparent (value achieved during the test run which is a straight average vs the value calculated upon reloading the data using the "mean" function), thus causing my investigation into the matter. 
So it appears "mean" and "average" are not really the same as the help file implies.  Is this intentional or a bug?
Thanks
David Jenkinson
Solved!
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Answer 1

david_jenkinson wrote:
So is there an internal "cast to double" in the mean vi function? 
Yes, there is a red coercion dot! (Watch for terminology: It is a conversion, nothing to do with casting!)
david_jenkinson wrote:
Also, if I'm understanding correctly, is not a conversion from single to double just adding zeros?
No, it is adding singificant amounts of mantissa bits to the representation, thus allowing more accurate computations for the additions and division. If you only have 6 significant decimal digits, every addition will be coerced to the nearest binary value. If you do that a few million times, the error will be large.
Look at the following example. Just reversing the array causes a significantly different "average", so which one is right?
(If you would do the same in DBL, the difference between the two results would be around 10E-9, i.e. insignificant.)
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