Centering the Data

If you can't change the values of the data, you can't do much.

If you want it centered around zero, subtract the mean from all data points. This will leave the relative values the same (difference, not ratio).

Taking the mean and removing the offset is the standard method of centering your data. This may not tell you what you want to know so a different analysis technique maybe warranted. Another analysis technique you should consider is taking a Fourier Transform of your data. You could calculate the standard deviation and perform a random process analysis to determine what random process is in your data. You could perform a least squares fit to see to a linear, exponential or other curve to analyze your data. A deviation from each type of fitted curve can identify if with a random process analysis can also be performed. A myriad of other regression analysis techniques are available that can reveal a hidden trend or attribute of your data.

I like to use deviation from the mean for some of my analysis.

http://en.wikipedia.org/wiki/Standard_deviation