I see that DVP [HERE and HERE] thinks the placement of the ruler is conclusive that it's pointing out the red smudge as the entrance wound, while others, at least at the Ed Forum, strongly disagree. Could it not be pointing out the vertical and horizontal dimensions of the large wound itself, rather than the red smudge?
Huh? What do you mean? There is no "large wound" visible in this autopsy photo below at all....so how could the ruler in the picture be "pointing out" any of the dimensions of the large wound (which, of course, was located on the right/front/top part of JFK's head, not in the rear of the head?

If it [the ruler] were pointing out the entrance wound, why did the autopsy doctors then place it 4" lower?
That's one of the questions we'll probably never be able to completely answer, along with this related question:
Why on Earth didn't any of the three autopsy surgeons (Drs. Humes, Boswell, and Finck) make note of the
precise "north/south" measurement of where the bullet entry wound was located on JFK's head? Just saying the wound was
"slightly above" the EOP is not nearly precise enough and has caused only further confusion and controversy concerning the President's wounds.
It seems particularly odd to me that the vertical (north/south) measurement for that head entrance wound was not fully documented, since the lateral (east/west) measurement
was specifically measured from a body landmark and noted in the autopsy report ("approximately 2.5 centimeters"). And 10 centimeters (or 100 millimeters, which is four inches) is 4 times as great a distance when compared to just 2.5 centimeters.
It makes no sense to me that the much larger north/south measurement was not noted or documented by the autopsy team, but the much smaller lateral distance was noted in the autopsy report. And we must remember that the Clark Panel in 1968, after viewing the original autopsy photographs and X-rays,
confirmed that the entry wound in JFK's head
was in fact located 4 inches above the EOP (see the Clark Panel excerpt below). Many CTers, of course, think the four-man Clark Panel was full of nothing but feces (and deliberate lies) when they wrote the following words:
"There is an elliptical penetrating wound of the scalp situated near the midline and high above the hairline. The position of this wound corresponds to the hole in the skull seen in the lateral X-ray film #2. .... On one of the lateral films [X-rays] of the skull (#2), a hole measuring approximately 8 mm. in diameter on the outer surface of the skull and as much as 20 mm. on the internal surface can be seen in profile approximately 100 mm. above the external occipital protuberance. The bone of the lower edge of the hole is depressed." -- Via the 1968 Clark Panel Reporthttp://jfk-archives.blogspot.com/2014/10/the-1968-clark-panel-report.html