[larsbrinkhoff]

If the device has opened a window, the scale can't be changed. This fixes the incorrect check against UNIT_DIS and improves error messages. Thanks to @markpizz for reporting the bug in #643

[markpizz]

You might want to include the (r != SCPE_OK) in the test before the reject reason, otherwise a bad numeric input won't have any explanation about the problem...

  if ((r != SCPE_OK) ||
+      (v != 1 && v != 2 && v != 4 && v != 8))
+      return sim_messagef (SCPE_ARG, "Scale can only be: 1, 2, 4, or 8, not: %s\n", cptr);