| You can use XL, you can use any mathematical calculator, or I am sure there are a ton of standard deviation calculators online to use. Just plug in your glucose values. It will give you the mean and sample standard deviation.
Let's say you plug in several glucose values from the past ten days and your average glucose is 100 and the calculated sample standard deviation is 10... what that means is that about 68% of your glucose values are from 90-110 (one standard deviation on each side of the mean, 100-10 to 100 + 10). Two standard deviations means that 95% of the time, your values are between 80 and 120. Three standard deviations means that 99.5% of the time, you are between 70 and 130.
The smaller the standard deviation, the less peaks and valleys. That's what you are aiming for.
I don't track it anymore, but when I was **** bent on gaining control, I had a three month average glucose of 88 with a standard deviation of just under 5, which is very, very tight control.
Standard deviation just completes the picture that an A1c partially paints.
__________________ "That which doesn't kill us makes us stronger" - Friedrich Nietzsche | 
