PLEASE I NEED HELP PLEASE

Question

something is really really driving me crazy for a few days now. i just couldn't figure out how this "standard deviation" function is going to work the way i like it to be! i am doing a science report. i read other peoples report, their graphs all shows normal "standard deviation"
i have this set of data over here. i calculated the standard deviation is about 5. and i input the value, it gives me this enormous bar. even if the SD is 1, still is a huge bar, who can help me out here????
i attach the file here.
http://www.2shared.com/file/kutjnIbJ/IIIIIII.html
to the button of the page, you will see "Save file to your PC: click here"

Answer 1

Davour wrote:
..but still, i calculated my standard deviation is like 4.6 or something, and still, the bar is quite big. but it is a lot of better than it was. however, does it only mean that my data is really inaccurate? i am no pro at this thing, but by looking at other peoples science articles of similar experiment of mine, their bars are only just tiny little bit.
Davour,
The standard deviation is a measure of overall variability, which is the actual variation in the things being measured plus the error in your observations. To determine where the variation comes from you will have to conduct a study of the error sources in your measurements. One way to do this is to repeatedly measure the same samples and observe how the measures vary on individual samples, plotting the standard deviation of measures for each sample in the set. The success of such a study depends on the stability of the sample set. For instance, does the standard sample naturally change in it's measurable quantity over time? It also could depend upon environmental factors beyond your control, or which you choose not to control.
You should strive to minimize measurement error when you can, and to document it whether you can improve it or not. Only then will you know where your variation comes from. Once you know this, you can estimate the portion of the total variation due to actual specimen variation.
Remember, low total variation isn't always good. It could mean that part of your measurement system is stuck.
Jerry