This scheme uses a binary nibble or byte, to represent each digit separately and then grouped together for more than 1 digit numbers (the first four digits are left unused):
4 would be 00000100
42 would be 00000100 00000010
423 would be 00000100 00000010 00000011
Slight variation on the scheme where two number are stored in one byte:
Two digits are stored in one byte
4 would be 00000100
42 would be 01000010
423 would be 01000010 00110000
Use of BCD in real life, digital displays, the final number output maybe delivered to the display unit as a BCD number to most easily compile into the display segments of the LED or whatever display type is being used.
Currency is often represented using BCD also due representation error.
Denary digits, translated to binary digits. Starting with the least significant nibble, if the added value is more than 9 then, add 6, to the nibble. The carried bit goes onto the next most significant nibble, carried across.
0.26
+
0.85
00000000.00100110
+
00000000.10000101
=
00000001.00010001