III is usually marked as 7A. This is mostly likely to be a II. There is a catalogue with lens diameters and you can measure it and compare the numbers.
This is an early series II, before Voigtlander cleaned up their act as regards identifying through engraving alone!
The "A" added to the size number for series III was a first attempt at differentiation. The "A" in this series (F.4.5) was given up when the series number was adopted in the barrel engraving. Series IV was always just a plain "Euryskop" - even though it was described as being for " full standing figures, groups ....".
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