Binary to Decimal

To begin by a simple example:
We have learned the dual system is extremely practical to understand the processes in a computer. Low voltage, high voltage is steadily occuring in it. (To claim it would "calculate by naught and one" is extremely exaggerated!). After all it is practical to convert its on-off signals to decimal numbers. How that can look is shown by the "truth table" aside.
A B C D is the binary part, the result of the processing in the computer with two distinct states on four lines.
On the right side of the table is the "Output" for us - readable ciphers from 0 to 9 - in the top line.
In the lower lines on the left side (High and Low, presented as 1 and 0); on the right side "1" means visible, "0" invisible.

How can it be realized?

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