By Maribeth Keane — I’m 61 now, and I’m an engineer. I was thinking if I ever wanted to collect something, I would probably collect slide rules because they’re small, they don’t take up much space, and they’re an engineering tool. Then one day I went on eBay thinking I’d just buy myself about 10 slide rules and put them in a little display case, and I bought a couple. I talked to some other collectors about if you had to have a slide rule, which one would it be? And I bought those. It kept expanding to the...