hi guys, I'm wondering in multivariate analysis, when we standardize our mean to 0 (centroid our data) why do we have to set our S.D = 1? I mean doesn't S.D = 1, only coves 50% of the data? shouldn't we use S.D = 3? where 99.95% of sampling data was covered instead? When we centroid our data, we've already lost some information, so why then do we still use S.D =1? can someone explain it to me! thanks!