Solved it!!

The following code works for me:

# Windows mouse wheel binding
$scale->bind('<Enter>' =>  sub {$scale->focus} );
$scale->bind('<Leave>' =>  sub {$mw->focus});
$scale->bind('<MouseWheel>' => [ sub { $scale->set($var+$incr*($_[1] /
+ 120))}, Ev('D') ] );
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If anyone with more experience than myself finds any potential problems with my solution then please let me know, I'm a complete novice when it comes to Perl-Tk bindings so I have no idea whether my code, while apparently working, might have some fatal flaws...