I believe that is the idea, yes.
The easiest way to test (assuming that you use the comma as the decimal separator) is to run the following two command lines, and ensure that the results are identical :
FLAC.EXE -o one.flac source.wav
FLAC.EXE -A tukey(0,5) -o two.flac source.wav
Edit: In fact, on testing, this appears to work even if you use a full stop as the decimal separator. I assume that Case is simply replacing any occurrence of "," with "." or something:
C:\Documents and Settings\Neil\Desktop>FLAC.EXE -o one.flac source.wav && FLAC.E
XE -A tukey(0,5) -o two.flac source.wav && FLAC.EXE -A tukey(0.5) -o three.flac
source.wav
flac 1.1.3, Copyright (C) 2000,2001,2002,2003,2004,2005,2006 Josh Coalson
flac comes with ABSOLUTELY NO WARRANTY. This is free software, and you are
welcome to redistribute it under certain conditions. Type `flac' for details.
source.wav: wrote 24487047 bytes, ratio=0.723
flac 1.1.3, Copyright (C) 2000,2001,2002,2003,2004,2005,2006 Josh Coalson
flac comes with ABSOLUTELY NO WARRANTY. This is free software, and you are
welcome to redistribute it under certain conditions. Type `flac' for details.
source.wav: wrote 24487047 bytes, ratio=0.723
flac 1.1.3, Copyright (C) 2000,2001,2002,2003,2004,2005,2006 Josh Coalson
flac comes with ABSOLUTELY NO WARRANTY. This is free software, and you are
welcome to redistribute it under certain conditions. Type `flac' for details.
source.wav: wrote 24487047 bytes, ratio=0.723