British use of the Austro-Hungarian maps

[Rockdoc]

I know that the only maps available to the French and British troops when they arrived in 1915 were those that had produced by the A-H before the War but they were found to be inaccurate. I have no idea whether the Struma valley was one of the last places to be mapped but I've come across what appears to be a map reference to an A-H map in April 1917, which seems quite late. It's in a signal recorded by 98th AA Section on 6th April, 1917 but there seems to have been some confusion about the plane's position:

1 Enemy plane flying from DEMIRISSAR to SALONIKA (9.15) NW of SERES about 10 miles (R states 14 miles NE of SERES Map Ref 41.41.8.4)

The writing is unusually large and clear and I'm quite happy that I've transcribed this accurately. I have no idea who or what 'R' might have been but 41-41 is the map covering the Struma. What 8.4 is I can't work out. Anyone have any ideas?

Keith