UPC is the retail barcode of the United States and Canada. UPC A carries a 12-digit product number, the GTIN-12; UPC E squeezes some of those numbers into 8 digits for small packs, by leaving out zeros. Like EAN numbers, they're assigned by GS1.

UPC A	UPC E
UPC A with a 2-digit add-on

What it holds
Characters	Digits only.
Length	UPC A: 11 digits, or 12 with the check digit. UPC E: see below.
Check digit	Always there. Type it or leave it out: Labeljoy works it out, and if you typed one it checks that it's right.
Modes	UPC A or UPC E.
Readable text	The digits, under the bars or over them, with the first and the last outside the bars.

Writing a UPC E. Type it as it's printed - 6 digits, 7 with the leading 0, or 8 with the check digit too - or type the full 12-digit UPC A, with or without its check digit, and Labeljoy shortens it. Only UPC A numbers with zeros in the right places have a UPC E form, and Labeljoy makes it for those that start with 0, the usual number system.

The add-on. EAN/UPC add-on, under the text to encode, adds a small second barcode of 2 or 5 digits on the right, as on magazines.

GS1 composite. A small 2D part above the bars for extra data: see GS1 and HIBC data. With it, the text can only go under the bars.

The rest of the settings are in the Barcode section. While the digits are printed the margins are part of the barcode, so the Quiet zone switch shows only with Text position set to Hidden.

What goes wrong
Invalid check digit.	The last digit you typed isn't the right check digit for the others - often a sign of a mistyped number.
This UPC-A number has no UPC-E form.	In UPC E: the number hasn't got the zeros a UPC E leaves out. Use UPC A for it.
A UPC-E starts with 0.	In UPC E: a 7, 8, 11 or 12-digit value has to start with 0.
Requires 12 characters in the input data.	Too few digits for a UPC A.
Invalid number of characters in the input data.	A UPC E value that is neither 6, 7, 8, 11 nor 12 digits long.
Input data too long.	Too many digits.
The EAN/UPC add-on must be 2 or 5 digits.	The add-on is the wrong length, or not all digits.