Like the Modern Analogue Technique, WA is a method for reconstructing past environmental parameters (temperature, pH) from a fossil assemblage, based on a training set of modern samples.
The (single) environmental variable, usually temperature, enters in the first column, and taxa in consecutive columns. All the modern sites, with known values for the environmental variable, go in the first rows, followed by all the downcore samples (these should have question marks in the environmental column).
The plot on the first tab shows all the modern samples, with the observed temperature (for example) versus the reconstructed temperature. This does not use cross-validation. The RMSE (Root Mean Square Error) is based on these values.
WA in Past follows Birks et al. (1990), with RMA deshrinking.
Reference
Birks, H.J.B., Line, J.M., Juggins, S., Stevenson, A.C., ter Braak, C.J.F. 1990. Diatoms and pH reconstruction. Philosophical Transactions of the Royal Society of London B 327:263-278.