Use of scale function

Normalization and scaling of analog signals
Hi, today I started studying the management of analog signals, a topic that I face for the first time .... I have come to a conclusion, I am explaining the reasoning waiting for any confirmations or denials.
So, I'm trying to convert Siemens teaching examples exposed in FBD to LAD, so I came across the following example, which shows the instructions NORM_X and SCALE_X:
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Assuming you have a tank to check, with a filling level from 100 to 1000 liters, and to have a transducer that outputs a 0-10V signal, this means that 0V corresponds to 100L and to 10V corresponds to 1000L and so far here we are.....
Now through the A / D converter present in my PLC the variable voltage between 0-10V is converted to binary, at the end I find myself a word inside the PLC that contains the digitized value of the voltage, for the S7-1200 this word contains values ​​ranging from 0 to 27648, as indicated to me in a figure in the PDF:
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First question: Why exactly this value 27648, where does it come from?
Then with the NORM_X function what you do is associate the numerical range 0-27648 (integer values) to the numerical range 0-1 (real values).
Second question: Why is this operation necessary?
Finally, with the SCALE_X function, in the example, what you do is associate the numerical range 0-1 (real values) to the variability range of the tank filling level or 100-1000L, so in this case thanks to the SCALE_X function I can understand the current value of the liquid in the tank, starting from a voltage value at the PLC input, right?