PrnCmp Basis

Selecting this button performs a principal components transformation
of the active variables in the data.

When projection pursuit is selected, this is automatically activated:
the 2-dimensional projection pursuit indices are designed for sphered
data, and currently this sphering is done by principal components.

There is no restriction in XGobi against using the projection pursuit
guided tour with unsphered data, but beware:  it may not produce sensible
results.

When sphering is turned on the tour history list is cleared because
the previous history pertained to the unsphered data.