Aztec is a square 2D barcode built around a bull's-eye in the middle, which lets a scanner find it with no margin around it. It's the barcode on airline boarding passes and many train tickets. Labeljoy also makes Aztec Runes, a tiny Aztec that holds a number from 0 to 255.

Standard

Runes

Modes
Standard	Any value Aztec can hold - see below.
Runes	A number from 0 to 255, in an 11 x 11 symbol. There's nothing else to set: Size, Error correction and Encoding aren't offered.

What it holds
Characters	Letters, digits and symbols, and the accented letters of Western European languages - é, ü, ñ and the like. The euro sign, other alphabets and emoji don't fit: use a QR Code for those.
Length	With Error correction 23%, up to about 3,800 digits or 3,000 letters. More error correction holds less.
Error correction	10%, 23%, 36% or 50%: at least that much of the symbol can be lost and it still reads. A new barcode starts at 23%, the level the standard recommends.
Readable text	None.

Settings
Size	Automatic size picks the smallest symbol the value fits. The sizes ending in c, 15c to 27c, are compact Aztec, the smallest; 19 to 151 are the full range, up to 151 x 151 modules. When the value doesn't fit the size you chose, Labeljoy uses a bigger one.
Error correction	See above. With a fixed Size it's greyed out: whatever room the value leaves in the symbol goes to error correction.
Encoding	Standard, GS1 or HIBC: see GS1 and HIBC data.

Characters you can't type. With Encoding set to Standard, a tilde followed by three digits is the character with that code - ~013 is a carriage return - and ~~ is a tilde.

The rest of the settings - quiet zone, color - are in the Barcode section. Aztec can do without the quiet zone.

What goes wrong
Input data too long. (Too many bits for selected ECC).	The value doesn't fit even the largest Aztec with that Error correction: choose a lower one, or shorten the value.
Only Latin-1 characters, the letters of Western European languages, fit in this barcode.	The value has a character Aztec can't hold - a euro sign, another alphabet, an emoji.
Numeric only data expected.	Runes: the value isn't a number.
Maximum input of 3 characters. Maximum numeric value 255.	Runes: the number is larger than 255.