Over the production cycle of the Model 617 Type 2 meter, the back plate exhibits two variants: On the left, the plate shows instructions and recommended film speeds for popular films of the time. The front of this model has the unit's serial number stamped on the meter face.

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The example on the right is the later variant. Proof of this is on the meter face which has six patent numbers listed, not just five. In place of the back instructions plate, it has instead a ceramic panel for marking up details of the film in use. The serial number is just below it. On the front meter face, the serial number is absent.​ Picture © David Paschke