Like others, I suspect you are asking about something related to Chinook. The compass correction card suggestion seems a good one.
Having now read what I think is the main technical submission to Lord Philip, I suggest you keep plugging away, but always bearing in mind one undeniable fact. The entire navigation system, not just your suspect system, had no operational clearance and was not to be relied upon in any way whatsoever. Maybe someone from the offices of ACAS and Group Safety would care to say why this fact was not passed to aircrew and, subsequently, the investigations. The submission to Philip demonstrates it was passed to ACAS. This single fact places the crews’ request for a Mk1 in an entirely different light and makes the claim about poor legal advice even more risible.