Bellerophon, if I may pick your brain a little further.
In your superb photograph you posted earlier in the Mach 2 Cruise level at FL600 I notice that both RMI'S shown seem to be showing a heading of 230 while the heading on the HSI shows 220 with the annunciation TRUE above the HSI.
Were you operating on TRUE headings in this case as it seems and what was the reason for this ?
I am thinking that the RMI's are showing magnetic headings ?