On my huge Cygnus run, the fft keeps failing in the deline code. It's actually pretty impressive, but there are 844604 points in the timestream. The prime factorization of 844604 is 2^2 * 211151. This is just damned bad luck, because I think an FFT is extremely inefficient when it can't factorize. What's the best workaround? .... 9 AM update: I've rewritten the deliner to work on a scan-by-scan basis. It's possible that the delining failed in the past because it was essentially removing a constant amplitude at the line frequencies across the observation (or combined observations!) which is not likely to be true.