Yesterday’s library technology is just a stealthy hunk of wood

Technology hasn’t always been bleepy-bloopy screens. It could really be defined as any new way of solving a problem. It could just be a wooden block with the name of the book that would be in its place with the proper the Dewey Decimal number written on it. In fact, that is precisely what the “book dummy,” from the Brooklyn Public Library is.
“A ‘book dummy’ recently surfaced at the Brooklyn Public,” the BPL wrote in a Tumblr post Tuesday. “This is a bit of library technology that has been obsolete for a while. ‘Radio physics’ for dummies!”

Book dummies were used when a book was too expensive or rare to be left on the shelf, and were kept instead behind the desk. You could bring the book dummy to the librarian and they would get you the real deal book.
This Ghirardi Radio Physics Course book dummy looks to be from, at the latest, 1933, when radio was still in its heydey and television had yet to take over. You can buy Radio Physics Course by Alfred A. Ghirardi (2nd Edition) on Amazon for $50.

Not completely outdated, the book dummy appears to still be in use at Hong Kong Polytechnic University library. Or you could order one online for $3.30 to $4.10. Man, the internet is wild.
People now would likely just look the book up online in a library’s database to find where it is. You don’t have to scan the stacks anymore in a specific part of the decimal system to find books that may be appropriate for your research (although boy is that fun!).
This is how technology moves on. Domesticating animals was technology once, and so was brewing beer. Everything has precedents. Before there was software as a system for libraries, before JSTOR, there were book dummies. Neat.