In a procedure, I'm defining a LOCAL series of k differences. When I call the procedure with 1 lag, say, the first entry is NA, and the rest of the series is the 1 period difference. When I call the procedure a second time (in a do loop) with 2 lags and print the series again, the first entry is NA, the second entry is identical to the first call, and subsequent entries are correct. I thought that defining the series as LOCAL would give me a blank slate on each call, and thus, the first two entries would be NA on the second call. Is there something else I should be doing?