(Please refer back to Shelf Balancing, Part 1 and Part 2 for context.)
I've got the numbers and I know what needs to go where. I've only been waiting for a few more sections to be weeded. There are several fairly large weeding projects in progress, so it's important that I don't start having any collections shifted until I really know how much space we're playing with. Here's how I figured it out, using the data in the spreadsheets I shared in Part 2 (except that here I'm sharing real data so I don't have to figure it out twice!)
The total percent of circulation of the non-fiction collection and the percentage of total shelves should be equal, according to Tony Greiner in his article "Collection Development and Shelf Space: A Proposal for Nonfiction Collections" (Public Libraries, November/December 2005, pages347-50). So, if the 200s make up 6% of the circulation of the non-fiction collection, they should get 6% of the available shelving in that collection. They do, within 1%. That section is good as is (although it will certainly get shifted as shelving is added to the ranges around it).
Dewey Range 000 currently takes up 42 shelves, which is roughly 4% of the total shelving available in the entire non-fiction range. Items in the 000 range make up roughly 8% of the total circulation of adult non-fiction. In order to balance 4% shelving to 8% circulation, I need to add 4% of the available shelving, or 49 shelves, to that range. (There are 1,012 shelves in the entire range of non-fiction.)
The biggest changes will be to the 700's - 21% of the circulation, currently on 16% of the shelves. I'm going off the numbers a little bit in this area to account for the huge physical size of art books. This section has fewer shelves per row because they are spaced more widely apart. I'd like to see about 25% of the shelves assigned to the 700's, which would be 253 shelves. I need to add 92 shelves to that range. That's a LOT of shelves!
Luckily, the 800s have had a nice big weed. Even more luckily, the 700s and 800s are back-to-back, so shifting will be easy. Can I take 92 shelves away from the 800s? No. I can take 85 shelves from the 800s because they currently have 15% of the total shelf space and only need 6%. The other 7 shelves will come from other areas (the 300s need to give up 35 shelves, for example.)
I will walk through the stacks, counting shelf by shelf and marking them so that those doing the shifting will know what call number should fall in what area. That way, they will know that they have shifted too much or too little before they get too far to fix it. I'll mark the bottom of every few columns or something similar to that.
In the end, the shelves will be re-balanced with the correct number of shelves allocated to each range of the collection. We shouldn't have to use the very top shelves in some areas and not in others.
My plan right now - and this could change - is to have the shifting happen at the end of the summer. We do a big full-building shelf reading project in August, and that would be the best time to do it. (I think...must ask others what they think of that idea!)
This has been such a fun project! I hate math, but I've really gotten into figuring it all out. Stay tuned for Part 4 when the shifting actually happens!