What is this?

This came from a lot of items from an estate sale, the guy had a massive parts supply and racks of misc equipment.
There's a strange lead coming out the rear, sort of looks like an electromagnet of some sort.
I didn't power it up not knowing what its used for.

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I looked up the TDK DC to DC converter and it seems to be used in a lot of hall effect circuits.
Could this be some sort of counter? Tachometer or sorts?
Frequency counter?
The bad part is I have no idea if or how the guy who had it used it, or if it was just a curiosity item to him that he kept.