What's happening to the card catalog?

Why have librarians been crowded around tables on Lower Level 1 and behind the library's service desks, sorting through index cards (and occasionally laughing out loud)?

For several weeks in February and March, HSL pared down its card catalog as a space-saving strategy in preparation for major construction in the Hammer Building later this year. It's very geeky and a little complicated to fully explain why this was necessary, but essentially HSL has discarded every card for which the same information can be found elsewhere. Many cards showed the same information that can now be found in CLIO, the Columbia University Libraries' online catalog. Much of what remains are card catalog entries for materials that exist nowhere else but at HSL. Below is a slide show displaying some of the more unusual cards that caught our eyes!