To account for the decay of the books, you need books that you know not only came from print shop x,y or z, but also you'd need to know how old the tools wee that made those books. Either that, or you'd have to have some understanding of how the tools decay from a theoretical model.
If you assume that the marks result from defects in the tool that accumulate, it should be relatively easy to build (and test) a monotonic model. Suppose we have an unordered collection of sheets, with some variable number of defects per sheet. If the defects are repeated (i.e. we can recognize defect A whenever we see it, as well as B, and so on), then we can build together paths- all of the sheets without defects pointing towards all of the sheets with just defect A, then defect A and B, and so on. There should be divergence- if we never see sheets with both defect A and C, then we can conclude the 0-A-B path is one tool (with the only some of the 0 defect sheets coming from that tool, obviously), the 0-C-D-E path is another tool, and the 0-F-G path is a third tool. (Noting that here 'tool' refers to one repair cycle, not the entire lifecycle.)
If you assume that the marks result from defects in the tool that accumulate, it should be relatively easy to build (and test) a monotonic model
The first assumption seems bad to me- I would assume defects accumulate only until equipment is reset or repaired, which is why I think you'd want some actual data.
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A list of some posts that are pretty awesome
I recommend the major sequences to everybody, but I realize how daunting they look at first. So for purposes of immediate gratification, the following posts are particularly interesting/illuminating/provocative and don't require any previous reading:
More suggestions are welcome! Or just check out the top-rated posts from the history of Less Wrong. Most posts at +50 or more are well worth your time.
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Note from orthonormal: MBlume and other contributors wrote the original version of this welcome post, and I've edited it a fair bit. If there's anything I should add or update on this post (especially broken links), please send me a private message—I may not notice a comment on the post. Finally, once this gets past 500 comments, anyone is welcome to copy and edit this intro to start the next welcome thread.