I'm doing a one-sample 3dMEMA analysis with two covariates (contained in a text file with the recommended format). Could you please clarify the following from the help file, under the -covariates_center option:

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If you want all covariates centered about their own mean, just use -covariates_center mean. Be alert: Default is mean centering!

So if the -covariates_center option is not called, will each covariate be centered about its own mean by default? If so, why would one need to "use covariates_center mean" as stated above? And does one simply type the word "mean", or the actual numerical means of each covariate? All the examples provided seem to be for two-sample scenarios.

I'm also not sure whether I need the -covariates_model option for a one-sample test.