"Position measurement diode" identification
I think you have an evaluation board from First Sensor.

There are links to the chips and information about the eval boards at that link.  Yours most resembles the DL100-7.  The DL100-7 has 1% accuracy.

The layout of the eval boards is very similar, but not identical.  I think you may have an older version of the board.
If TP8 and TP9 are disconnected, then your module isn't wired like the current eval boards.

Maybe you can ask for info on old boards (or find them in an archive on the site) or maybe you should just purchase a new device with known characteristics  - it is also entirely possible that First Sensor is a competitor of the company that built your module.

A quick look around doesn't find any one else building PSD eval boards in that form factor, though, so it ought to be First Sensor.