This post was really helped us to solve an initially baffling problem.We use a macro to calculate a check sum on the *contents* of SAS datasets in order to be able to identify the datasets when we transfer them via SAS V5 transport format. The transport file is sent along with the check sum and the recipient extracts the dataset, re-calculates the check sum and compares to the original. We were getting differences where there should have been none. It turned out that the difference were negative zeros which were converted to positive when creating the SAS V5 transport file because this uses an IBM standard for numbers.