Turret Position Indicator?

I have just bought this gauge from Jet Art for the DH108 RH instrument panel that I’m drawing up…

http://www.ebay.co.uk/itm/RAF-RN-Aircraft-Turret-Position-Indicator-170FC-With-Original-Packaging-/130954607168#ht_1114wt_1161

It matches well the pair that appear in the cockpit photo that is published in both DH.108 books that are out there (one by Brian Rivas, the other by Henry Matthews).

Any idea what this gauge is? What it is from? I would have thought a turret position indicator would have four cardinal points. Perhaps someone knows their Smith’s codes well? FC=?

Cheers.