Sure I do. You are asking what unit of measure Noah used to build the ark. You are assuming it was a cubit, BASED ON THE LENGTH OF NOAH’S ARM TO HIS FINGER. Then you ask how anyone could know what the length of a cubit was in Noah’s day, or the length of Noah’s arm. The fact is, we don’t know what form of measurement Noah used. God told Moses to use the term “cubit” in describing the measurements of the Ark. That would be EGYPTIAN cubits, of which we certainly know the length of.
And how did Noah use Egyptian cubits when he predated the Egyptians? Perhaps you are thinking that the Egyptians somehow learned of Noah’s arm length and couldn’t resist adopting a unit of measure from the Jews.
No, I am asking how someone can look at what he presumes to be a shipwreck and say it is exactly 300 cubits long. We really don't know if Noah's cubit and the Egyptian cubit are the same; and, I am betting they are not. This post should be combined with the previous.
Please also note that, according to Wikipedia, the Egyptian cubit rods range from 44.4 to 52.92 cm in length. That is a rather variable constant.
As a final comment, using “approximately” instead of “exactly” would rectify the situation.