On 16-11-2010 15:48, Invisible wrote:
>>> Does anybody here know enough about statistics to come up with answers?
>>
>> That's what standard deviation (σ) on my old casio FX-180P is made for.
>
> The standard deviation tells you how variable something is. However:
>
> 1. This, by itself, does not tell you how many measurements you need to
> take to achieve a given level of accuracy.
>
> 2. If you compute the SD from the data you gathered, then the SD itself
> may be inaccurate.

IANAS but the SD is expected to go down with the square root of the 
number of measurements *if* the data is from a normal distribution. So, 
if that is the case (or can be assumed to be the case, then you do a 
limited set of measurements and divide that by the required SD, the 
square of that should give an estimate of how much longer you have to go.

If the data is from a different distribution, you have to know that 
before you can compute anything.

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