If it doesn't turn up and you have a laptop, you can find an emulator for one. They're a PITA compared to the real thing, though.
No laptop, and no one uses them in classes at my college anyhow.
I'm pretty sure i know exactly how it got lost, assuming it did. As soon as people started getting up to leave my physics class, people started rushing into the room so they could sit down for the next class to begin. I thought it was pretty rude, and tried gathering my things quickly and shit so I could get out of there. I'd imagine I left it on my desk or something if that's the case.
I just really hope it turns up

I'm going to look around my house for a bit more, and then post a 'lost calculator' email out to the student body at my college. I'll give a $20 reward for it, but I doubt anyone who'd thieve a calculator like that would give it back for $20.