Standard Deviation from one sheet to another

[Pezzzz]

Hi all

I have a workbook dealing a large amount of logged Data over a period of 4 months and counting. I want to take the standard deviation of the temperature readings, for each individual day. I have a 'Data' sheet which has readings for temperature taken roughly every 3 minutes with their corresponding date/time. In a second 'Results' sheet I have a set of results calculated for each day which is where i want to formula to go . There are in the region of 500-700 readings taken each day, the exact number taken is recorded in the 'Results' sheet.

I am running Excel 2007, on not the fastest machine.

Any help would be greatly appreciated.

Josh

 

[Pezzzz]

Here is some more info of what I have tried. I meant to put it in an edit, but those are only allowed before 120mins...

STDEVP, This function would be perfect, although it lacks the ability to choose the correct temperatures to calculate.
IF, If commands require a false input for the case that the date is incorrect. I can't use zero, as this will destroy the average part of the deviation. Using "" to give nothing seems to cause my final formula to also give nothing as the final answer.
DSTDEVP, I was unsure of the syntax of this formula and was therefore unable to get anything of use out of it.

As far as i can tell STDEVPIF would be perfect if it were to exist, but it doesn't.

For those who are unsure SQRT(VAR( will give the same value as STDEV..

Finally the formula for STDEV in maths terms is as follows.

SQRT((SUM(x-X)^2)n)
Where:
x is each of the values
X is the average of all the values used
n is the number of values used

Regards

Josh