OK, so if those two data sets were poker session results in dollars for two different players although they've both made the same amount of money player 1 is the 'steadier' player with a lower standard deviation - am I right in saying then that the standard deviation for those two players would be 2.23 ($2.23)?
In order for a standard deviation to be defined there has to be enough data so that a bell shaped curve can be seen on a graph when plotted. You can not have a sample size of three points and get a graph. Well you can but it will not be meaningful.
The range of possible points need to be taken into consideration. So taking the wiki link in C9's 1st response
http://upload.wikimedia.org/wikipedia/commons/f/f9/Comparison_standard_deviations.svg there are 2 different graphs overlaid on the same chart, showing 2 different standard deviations.
So a standard deviation is some value that represents a deviation from the average over a sample data set. If we use trackers for our poker data set we approach a perfect data set and a Standard Deviation can be defined, or agreed upon over a large sampling.
But you could be sampling cars colors as a game with you kid while you drive between Kansas City and Tulsa. She counted maybe 1000 cars and plotted them on a color basis and found that 60% were either black or white. You might determine that the 60% number constitutes a standard deviation if the numbers show that the black/white ratio was approximately equal. If so then a standard deviation could be defined as 30% (either way on the graph) and a pink Mazda with Flames (you saw 1) is not within the standard deviation, but does represent one extreme on the graph, while a yellow bug with Tall tree painted on it (also saw 1) would represent the other extreme.
SO .....
Your head has exploded and your eyeballs are looking for a socket to hide in.
Point is that for the most part you need a bigger sample size and a definition of what you are plotting before a standard deviation can be determined and thus possibly useful. :embarasse