Code 39

Code 39 (also called Code 3 of 9) is one of the oldest alphanumeric 1D barcodes, encoding uppercase A–Z, digits 0–9 and a few symbols; it is self-checking but relatively low density.

How it works

Each character is made of nine elements — five bars and four spaces — of which three are wide, with an asterisk marking the start and stop.

Where it's used

Common in industrial, defence, automotive and government inventory systems where robustness matters more than compactness.