In my textbook it says the data is assumed to be zero-centered. I am not sure what this means. I read it stand for substracting the mean from the individual values, however I would like to know do you divide the values by the standard deviation as well.
For example if one dimension had values 8 10 12 and another 80 100 120, the latter would have much more variation and consequently PCA would assign it a greater weight. My question is whether we divide the data by standard deviation as well.