binary coded decimal (idea) by bitter_engineer

Also known as BCD. This is a way of using four bits to count to 10.
Zero is 0.

This is inefficient, of course, but it is useful in a couple of areas:

Making drivers for 7 segment LED displays. Instead of using one byte for each digit on the display, you can stick two BCD numbers in each byte, and halve your required space.
Accounting software. If you want to be accurate to the penny, then you need to work in the same base system as the currency. Calculating 1/5 in binary will leave you with a repeating fraction, which does not happen in the decimal system. Calculating 1/16 in binary will leave you with a number that does not get rounded, which does happen in the decimal system.

Binary-coded decimal	binary clock	Hexadecimal to binary	BCD
Double space after a period at the end of a sentence	Gray code	Stream Cipher	applet
binary	gnome	Work like you don't need the money	NaN
hexadecimal	automatic BCD	repeating decimal	E2Parents
Convert base ten to binary	biquinary	IP subnetting	opcode
Notation	character set	diagonal argument	decimal