Hmmm, the only chocolate bars I ever had were rectangular. (As an aside, in the plot in my previous post, I extended the intercept line in the direction of the celestial body with an arrow ending with the symbol of the celestial body. In this instance the sun. That practice was fading into disuse, but some yachtsmen liked doing it on their chart paper. The EP was a point on the LOP that was at the shortest distance between the DR and the LOP line. Probably that's why a little square was used because of the right angle formed between the intercept and LOP lines? Just a guess. Other than that, the EP has little meaning. This was the practice used back in the 1970s.)the only thing square in my time was a piece of a chocolate bar:
Anyway, I was taught that the course made good can only be determined after a second fix is obtained, after which you can then get the set and drift of the total average current that affected the ship by comparing the DR of the fix to the actual fix itself. Yes, if know the current you can compensate for it by adjusting your course for it. Did that all the time in my flying days using predicted winds aloft.
Anyway, the log doesn't measure current, only distance travelled through the water. If the ship was making say 22 knots at 75rpm through the water, and if there was a head current of 1 knot, the log would still measure an advance of 22 miles each hour assuming it was accurate. And let's not forget that Boxhall said that he thought the ship would reach the corner some "considerable time" before 5:50pm. To me there had to be some indication to him that the vessel was running ahead of her DR, not behind it, after he came on duty at 4pm. Unless, of course, you want to believe that he was outright lying about that?