German WW 1 artillery tool

[ulaire]

I recently bought this tool. Really not my normal area of collecting, but they told me it was for German WW 1 artillery.
Up till now, I haven't been able to find more info on what it is precisely, so any info would be more than welcome.

Diameter is 14cm.
Center has some sort of see through crosshair.
Numbers on the outer rim go from 0 to 64 (or 6400).
Numbers on the inner rim go from 0 to 400.
Movable part has a scale from 0 to 10 for the upper part and 0 to 50 for the lower part (and neither of them exactly match the corresponding scale on the ring for some reason).
Marked with the code: 4./I.R.8.1.

 

[Weasel Pilot]

The outer scale is mils (6400 mils in a circle). Perhaps a quadrant used in laying a piece of artillery? The two oval depressions MAY have held a bubble level

 

[Natter]

It's a map-protractor for artillery: "Kartenwinkelmeßer 140 mm Durchmesser" (K.W. 140 mm Ø). As you can see, a part has been broken off.

There were also a 200 mm diameter version.

I'm not sure when these entered service with Wehrmacht, but I think it was in the mid 1930's.

The marking suggest your instrument belonged to the 4. Zug (or more likely batterie) of 1. Bataillon, 8. Infanterie-Regiment, which was attached to various Infanterie-Divisionen from it's forming in 1992 up to being converted to 8. Grenadier-Regiment in 1942. Attacahed photos are from an old online auction and the german manual.