Odd hydraulic motor or pump?

A few years back I picked up some interesting bits in a junk shop that only came to light again during my aborted move, and I'm still not
sure what they are. Hard to describe but here goes:
A cast iron cylindrical body about 3" diameter and 3" long with a mounting flange at one end with a shaft protruding on the axis of the cylinder. An inlet and outlet port set tangentailly to the outer of the cylinder. Dismantling, the body is parallel bored showing pockets cast by the two ports, with a cylindrical rotor on the shaft which is a nice fit in the bore. Across the rotor (rather akin to the gudgeon pin in a piston) is another cylinder that slides from side to side as the rotor rotates due to an offset pin arrangement anchored to the end of the main bore opposite the flange. If oil were to be forced into the inlet it would make the cross set cylinder slide, which would rotate the main rotor which might suggest thst it is a motor, but it seems a very complicated way of making one. Similarly if the rotor is turned by hand, oil can be transfered from inlet to outlet though it seems a bit erratic.
Now the question. Is this a hydraulic pump, a hydraulic motor, or perhaps some form of metering device ?
I was raking over the pile of 'too good to throw away' bits looking for a small gear pump for an oil transfer application when I remembered these 'things' - I have about half a dozen of them, brand new never used - I think I got them at Anchor Supplies in Nottingham about 15 years ago.
AWEM
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Is there a difference? I used to know a power station where "hydraulic motors" were used as jacking oil pumps.
For that matter, any positive displacement pump is a metering device if you count the revs.
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