Output on TTY with
- ENCODING set
- binmode set

(TT expects utf8 for input and produces uft8 output)

$ perl tt.pl
Var = abcdef

6   # prints 6
fööbä  # prints "fööbä"
fööb  # prints "fööb"

==================================
Output with
- ENCODING set
- binmode NOT set

(TT reads UTF8 properly, calculates correctly, but produces iso-8859-1 for output)

$ perl tt.pl
Var = abcdef

6   # prints 6
f??b?  # prints "f??b?"
f??b  # prints "f??b"

==================================
Output with
- ENCODING NOT set
- binmode NOT set

(TT expects iso-8859-1, gets UTF8 and uses it without conversation, calculations are incorrect due to false expectations of TT, TT outputs as ISO-8859-1 without conversation thus printing the UTF8 chars correctly "by accident")

$ perl tt.pl
Var = abcdef

9   # prints 6
föö  # prints "fööbä"
fö?  # prints "fööb"