Ah, but what is it? [1] A few hints are in order...
I paid roughly the same price as an HP35 cost when it was introduced. Fairly rare; there were far more HP35s produced. Older than an HP35. But is bigger[2] than an HP35 and was in production for significantly longer.
I certainly wasn't going to have it posted, so I retrieved it myself from the auction house.
[1] I've already tantalised denizens of another forum, so I'd appreciate it if they didn't spoil the fun here
[2] Probably the biggest calculator, short of an old mainframe computer, that has ever existed or will ever exist. There are several in the attached picture.