@Lonewolf and vaneyck:
More to the point: if you have an aircraft flying in a known pitch/power combination that is sustaining level flight and stable speed quite happily, why use approximations from the book in the first instance?
If the aircraft had been upset and at the same time airspeed became (or was already) unreliable then it is understandable, as it at least gets you back to a ball-park figure, but surely the crew were not so absent-minded as to have not made a mental note of the current pitch and power? They are, after all, supposed to be flying the aircraft?