A comparison of Jessica’s handwriting and the Rubaiyat’s inscription
This subject was covered years ago either on Reddit, the Smithsonian or another blog*, either way finding it now is a bit of an ask so what better than rehash the subject here and have it more readily available.
Basically, what we are doing is comparing the V70 inscription with known examples of Harkness’ handwriting, samples of which are below.
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The inscription, believed to have been written by Jessica.
A letter known to have been written by Jessica.
Another letter known to have been written by Jessica
The trick, apparently, is to find three or four examples of the same letter in the inscription, the letter I, say, which establishes a pattern, then compare it to the same letter as written in the correspondence. Repeat about half a dozen times with different letters then do the numbers. That’s about as scientific as it gets.
*Cramer, ever the reactionary, has just resurrected a couple of posts on the same subject, probably worth visiting but don’t tell him I sent you. Unlike him though, I’m going to let you do it for yourself.
The Somerton Man 
If you use this software you can compare the handwriting. If they are the same person the scores should be close to 25%, 25%, 25%, 25% if all 4 samples the same (3 above and the code). If one is saying 4% or similar then that one is likely to be a different person.
https://www.csmc.uni-hamburg.de/publications/software/hat.html
I used this software to compare the handwriting of the hotel cards for the Isdal Woman and it identified that the last one was significantly different.
The reason?