Codabar

Codabar is an older self-checking numeric barcode that uses four start/stop letters (A, B, C, D) and was designed to print easily on early equipment.

How it works

It encodes digits and a few symbols with a simple bar-and-space scheme and needs no check digit, though one can be added.

Where it's used

Still used in libraries, blood banks and blood-donation tracking, photo labs and some logistics applications.