# mouse wheel

            self.bind('<4>', lambda evt: self.increase())

            self.bind('<5>', lambda evt: self.decrease())

            # modified mouse wheel

            self.bind('<Shift-4>', lambda evt: self.increase(multiplier=0.2))

            self.bind('<Shift-5>', lambda evt: self.decrease(multiplier=0.2))

            self.bind('<Control-4>', lambda evt: self.increase(length=1))

            self.bind('<Control-5>', lambda evt: self.decrease(length=1))

        self.last_level = None  # used for muting

    def set_var_rounded(self, value):

        """use this instead of just self.fade_var.set(value) so we can

        control the precision"""

        # this was just to make the display not look so weird, but it

        # could actually affect the speed of really slow fades. If

        # that's a problem, do a real trace_write hook for the

        # variable's display instead of using Label(textvariable=var)

        # and format it there.

        self.fade_var.set(round(value, 7))

        if self.fade_var.get() != value:

            self.fade_var.set(value)

    def fade(self, value, length=0.5, step_time=10):

        """Fade to value in length seconds with steps every step_time

        milliseconds"""

        if length == 0:  # 0 seconds fades happen right away and prevents

            # and prevents us from entering the fade loop,

            # which would cause a divide by zero

            self.set_var_rounded(value)

            self.fading = 0  # we stop all fades

        else:  # the general case

            self.fade_start_time = time.time()

            self.fade_length = length

            self.fade_start_level = self.fade_var.get()

            self.fade_end_level = value

            self.fade_step_time = step_time

            if not self.fading:

                self.fading = 1

                self.do_fade()

    def do_fade(self):

        """Actually performs the fade for Fadable.fade.  Shouldn't be called

        directly."""