I agree with everything you just said Jim. But I'm sure you have to agree that the deviation error on a given compass is not likely to change by any significant amount over the course of a 4 hour period under normal conditions. But speaking about deviation error, Boxhall discovered that the ship was following a true course of 266° when in fact it should have been on a true course of 265°. I suspect that was after he obtained a correction to the deviation error of the standard compass that night. This of course was done after the ship had altered course at 5:50pm, and so it would sense to check the deviation while on that new course. Which brings me to what I wrote several posts earlier. It seems Murdoch was more interested in seeing an update to the deviation error than having an extra pairs of eyes out on the bridge as they were about to enter the ice region.The Deviation error of the steering Compass is not the same Deviation error as experienced by the Standard Compass. Magnetic Compasses are individual units with errors specific to each and the compensating elements are located at different distances relative to the compass needle.