That funny check-numbering font

Posted April 22, 2005

Broadening my education some more in the "wow, I never realized that" sense. In case you had ever wondered why checks use that strange "computer-ish" font for the routing and account number information, this is why.

The font characters were specially chosen so that when printed in magnetic ink, they would each have a unique signature when scanned horizontally by a one-dimensional read head. So they needed to change a few line widths and so forth to make sure that, for instance, the 2 and the 5 would look different (since in a classic 7-bar LED font the two would have identical vertical projections).

The interesting part is that it's possible to buy ink-jet cartridges now that use the same magnetic ink, so you can (a) print your own checks and still have them get properly scanned by the banks, and (b) have a general alternative to optical bar codes that is both human- and computer-readable in a transparent way. The ability to read the code without direct sight might also be an advantage, if for instance you wanted to scan an identification code inside of a sealed envelope for some reason.

Note that the ink is magnetic, but not magnetized. That is, the reader needs to have a magnet to align the ink particles prior to scanning, as opposed to a classic magnetic swipe-card whose data is semipermanently encoded and just needs a passive reader head to scan it.