How can I understand my standard deviation?

Question

I have some (2749) senor output values. They range from 0 to 1769. With google spreadsheet I put it thru some calculations to get the (mean) average and standard deviation. With this I created two colums BINS and NORMDIST to create a chart. Please look at the attached image.

Mean is 53.35. Standard deviation is 61.23

What can I extrapolate from this?

Is one deviation 61.23, two deviation 122,46? Two deviations gives me ~95%. So since my mean is 53, 95% is a range from 0 til 122?

My chart shows while the range is from 0 to 1769, its mean is 53. Is my data bad? The form of the curve the data makes is very "typical" distribution, but a little skewed to the left?

STDEV

Answer 1

1. I think that you can simply ignore data beyond 3σ (usually you don't need more precise results, because you have 99+% probability that each new result will be in 3σ range from the peak of your distribution).
2. Then try to repeat your calculations without "unnecessary" data (those that lay beyond 3σ). Maybe it will lead to better result.

Each experiment has its own appropriate precision. Your data can be too precise for one experiment and nearly useless for another; depends only on the kind of experiment.