# Precision of estimated parameter using standard deviation

Consider a set of samples $S$ containing measured samples. From this set, a series of values indicating pressure are derived. Now, a variable X is estimated by taking the maximum value of all the values indicating pressure ($P_{max}$) and subtracting from it the minimum value of all the values indicating pressure ($P_{min}$).

So, it’s something like that:

$X = P_{max} – P_{min}$

Now, I want to find the precision of my estimation and therefore I am thinking of using the standard deviation (SD). However, it gets a bit confusing as to how to derive it.

From what I understand, there is no point in trying to find the SD from the $P$ values used for deriving $X$. I should probably repeat this procedure a number of times, derive say five $X$ values and then find the coefficient of variance among them. What do you guys think?

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