====================
Moving Current Value
====================

The tkinter Scale has the ability to display a moving Label with the current
scale value. One might think of a Canvas with a moving value, but we shall 
use an ordinary Label positioned according to the ``place`` layout manager.
The current Scale value is known, the main unknown is the 
position of the display Label for any given Scale output, this should 
correspond to the centre of the slider which is offset to be above the Scale. 
Since both ``rel_min`` and ``rel_max`` are known it should be easy to calculate.

Just as with the
range values use a relative ``x`` value. As the cursor moves so the current 
value in the display value should change - check what is 
required by moving the tkinter Scale. To keep the display label 
updated use the ``command`` option on the
Scale, this calls up a function that calculates the relative ``x`` and 
simultaneously sets the display labels position and actual display value.
Otherwise linking the display label through a tkinter variable, but would show
a float number with umpteen decimal places. 
Every slider movement triggers the function, so a continuously moving and 
changing display results. Link the SpinBox and
Scale through a tkinter variable, then adjust the Spinbox's size to limit the
its display. 

A simple function is used to calculate the relative x position::

    def convert_to_relx(curr_val):
        return ((curr_val - from_val) * (rel_max - rel_min) / (to_val - from_val) \
            + rel_min)

Another function changes the display label::

    def display_value(value):
        rel_x = convert_to_relx(float(value))
        disp_lab.place_configure(relx=rel_x)
        disp_lab.configure(text=f'{float(value):.{dig_val}f}')

.. note:: There are several methods to format text, the latest configuration 
    for Python 3.6 and above is the preferred method. Value (Scale actual 
    value) needs to be converted to a float. The ``digits`` option, dig_val 
    is related to the number of decimal places shown. Since a float 
    is being replaced the variable ``dig_val`` requires curly brackets.

.. container:: toggle

    .. container:: header

        *Show/Hide Code* 07ttk_tkinter_shift_value.py

    .. literalinclude:: ../examples/scale/07ttk_tkinter_shift_value.py
        :emphasize-lines: 17, 36-38, 40-45, 47-48, 50-51, 53, 67, 70-73, 75-77