grofit package model validation


I used the grofit package (gcFitModel) for my data and obtained values for A, mu, and lambda. Its possible to easily do a cor.test for my observed data and the parameter I get for A (asymptotic size), but I am unable to figure out how to validate either all my parameters at once, or also the mu and lambda using my original data. I tried using the CAVIAR package with fitGompertz, but I was unable to reproduce the examples that they have there and their package explanation is far from clear... If anyone knows how to validate a Gompertz growth model using the output from R, it would be greatly appreciated (R2, MSS, etc). Thank you.