[TG] [TG11] ST2000+ not heading correctly in track mode

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Hi There,
I have an ST2000+ tiller pilot interfaced (by via ST1 to STNG converter) with ST60+ instruments and an A70D Plotter/MFD.
Communication seems to be working ok, pilot pop ups appear on the ST60 displays and wind and track data appear on the ST2000+ When it is in the appropriate modes.

I can set up a route or waypoint and enter in to track mode ok.
However, I have noticed one glitch when the autopilot is in track mode.

Although BTW, Heading and COG all appear to be sensible, the autopilot seems to want to head 10-15 degrees to port of the BTW. I have tried this on a range of track headings.
I suspect that the error is that magnetic variation (about 13E here) is being applied once too often somewhere in the system.
I have variation in auto on the ST 60+ Graphic and on the A70D plotter.

Could you please advise the correct variation settings for each instrument/display and let me know if there are any other configuration changes I should check out and correct?
I am planning further test in the next few days, so if there’s anything I need to do to get you more data to work with please let me know.
Regards
Dave Davies.