# What is this thing, and why is it there?

**URL:** <https://boards.straightdope.com/t/what-is-this-thing-and-why-is-it-there/238390>\
**Category:** Factual Questions\
**Created:** [April 5, 2004, 5:32pm UTC](https://boards.straightdope.com/t/what-is-this-thing-and-why-is-it-there/238390 "2004-04-05T17:32:43Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![dnooman](https://avatars.discourse-cdn.com/v4/letter/d/839c29/32.png) [@dnooman](https://boards.straightdope.com/u/dnooman)\
**Post date:** [April 5, 2004, 5:32pm UTC](https://boards.straightdope.com/t/what-is-this-thing-and-why-is-it-there/238390/1 "2004-04-05T17:32:43Z")

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I’m sure this will be answered quickly, it’s probably fairly well known. I have no idea what to call it, but I think it’s coding of some sort. In the bottom right-hand corner of some papers that my new employer sent me, there is a little box maybe 1/4 in square, with lots of little black dots arranged like a really complex barcode. I supect this is either coding for the actual text of the letters, or is a reference for the copier. I’d have googled this, but like I said, I have no idea what it’s called.

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**Author:** ![av8rmike](https://avatars.discourse-cdn.com/v4/letter/a/edb3f5/32.png) [@av8rmike](https://boards.straightdope.com/u/av8rmike)\
**Post date:** [April 5, 2004, 6:07pm UTC](https://boards.straightdope.com/t/what-is-this-thing-and-why-is-it-there/238390/2 "2004-04-05T18:07:23Z")

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You are pretty much right. Does it look like [one of these](http://www.adams1.com/pub/russadam/stack.html)? If it is what I’m thinking of, it’s a Data Matrix two-dimensional bar code.

As to what could be stored in it, I have no idea. Looks like many of the links on that page are outdated, but probably nothing some basic Googling won’t turn up.

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**Author:** ![dnooman](https://avatars.discourse-cdn.com/v4/letter/d/839c29/32.png) [@dnooman](https://boards.straightdope.com/u/dnooman)\
**Post date:** [April 5, 2004, 6:18pm UTC](https://boards.straightdope.com/t/what-is-this-thing-and-why-is-it-there/238390/3 "2004-04-05T18:18:59Z")

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Yep, it’s a Data Matrix. I don’t know what’s in it either. It’s from Merck, so it’s probably some silly form letter reference.

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**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\
**Post date:** [April 5, 2004, 9:25pm UTC](https://boards.straightdope.com/t/what-is-this-thing-and-why-is-it-there/238390/4 "2004-04-05T21:25:13Z")

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I did a little work on the PDF (not the same as Adobe pdf document) 2D symbology; it is really interesting in that it can be encoded with differing levels of redundancy; at the highest level of redundancy, a large portion (any two thirds IIRC) of the barcode can be torn off or otherwise obscured/obliterated and it can still be readable.