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Correlations

This object records the (symmetric) matrix of correlation coefficients between parameters in the most recent least squares fit. There can be at most one of these; it is automatically created if not present and updated on every fit.

This is used to estimate the uncertainty in calculated line positions, provided  ShowEstUnc is set at the top level. It can be edited in the constants window. To add or remove entries right click on the "Correlations" label and select resync; this will adjust the matrix so that every parameter marked as  floated has a corresponding row and column in the matrix.
 
For compatibility reasons the correlations object was only written to the .pgo file in versions 8 and before if ShowEstUnc was set.