Disclaimer: I have zero formal training in audiology, know nothing about military disability processing. I have never met a Rudmose audiogram-- But I do know the name, from sound reinforcement studies. (Wayne worked a wide field.)
Rudmose made many audiometers, but this looks like one of his recording audiometers, 1950s-1960s.
A beep is presented to S (subject). If S hits the button, level is reduced; if S does not press, level is raised and beep repeated. After a few trials the levels tend to be “around” S’s true threshold. After 10-12 tests at one frequency, it moves to the next frequency; after one ear, the other ear. All levels are plotted on a card.
So the “true” HL is the average of the later (more right, more-even) jags.
“Normal” is to 15HL, “Mild” to 25HL. These definitions are arbitrary and have changed with circumstance. I doubt the Navy would be concerned about 25HL.
The 1968 gram shows an almost-moderate 35HL at 4000Hz left. This is not atypical in men, even young (I was losing some by age 15).
Your interest is how much was lost from 1968 to 1973. I fiddled with the graphics to get the two on the same pane.
Yes, it says 10dB more HL at 500Hz. However 20HL is such a low level, and 500Hz a low frequency, that this may be contaminated by background rumble (nobody could hear under 20HL in that test room). Left shows a 10dB change at 6000Hz except it is inconsistent from the first few tones to the last half of this sequence. Right ear shows IMprovement at 4000Hz; or a thumb twitching from 9 minutes of stupid ear-tones; or tinnitus in this area.
What you expect to see after 5 years of big noise is maybe like this:
But that is not what you have.
In my NON-Expert opinion: the audiograms show little or no hearing loss '68-'73.
I believe that in recent years more experts understand that hearing loss is not right away. That short term damage “that gets better” actually sets the stage for earlier onset of hearing loss in later life. Of course this is impossible to prove in humans, and is not popular with benefits policy-makers.