Hi Bob,
I can only speculate, but the VBA author might have been trying to determine the number of elapsed days between two dates, and used the number of weeks since 1/1/1900 as the basis for that calculation (i.e. number of weeks divided by 52 to get years, then the number of years times 365 to determine days, etc.!).
Of course, there are many simpler approaches for calculating elapsed days, and as such, I am not sure why anyone would use such an approach. It could be that the VBA author did not want his "secrets" to be revealed to any casual reader of the code! Or, it could be that the VBA author did not know what he was doing. Either way, it adds to the enjoyment of those reading his code (which could have been his/her motive!)
Cheers,
Sajan.