Hi: I am trying to migrate from Systat to R but I am facing my first challenge. While I easily can get weekly co-variance for my data, I can't seem to acomplish this with R ( I can't figure out how is done) If interested in looking a sample of my data, please check the Excel attachment. In Systat from Week 28 I get a covariance of 1055 fish. Thanks in advance Felipe D. Carrillo Fishery Biologist US Fish & Wildlife Service Red Bluff, California 96080 ---------------------------------