The variables IDVOUT and IDVERR specify device numbers for ``running output" and ``error messages", respectively. Normally these would both be set to the device number for ``standard output" (e.g., writing to the screen if running interactively). The variables IDVOUT and IDVERR are set by DATA statements in the ``main" program DDSCAT.f and in the output routine WRIMSG (file wrimsg.f). Under Sun Fortran, DATA IDVOUT/0/ results in unbuffered output to ``standard output"; unbuffered output (if available) is nice so that if you choose to direct your output to a file (e.g., using ddscat >& ddscat.out &) the output file will contain up-to-date information. Other operating systems or compilers may not support this, and you may need to edit DDSCAT.f to change the two data statements to DATA IDVOUT/6/ and DATA IDVERR/6/, and edit wrimsg.f to change DATA IDVOUT/0/ to DATA IDVOUT/6/.