i am still confused about the ketuba. in the Mishna in Demai chapter 2 mishna 5 the commentary of the rambam says a dinar is 6 zuz. and the dinar during the time of the mishna was the roman danarius. which was about $8,75 so a zuz is about $1.50. so that is about $300. [each zuz was in weight 16 grain of barley. so this works out ok. ] but what to do with the Rambam in Laws of Shekalim where  one shekel is 284grains of barley weight in silver? [and 20 zuz is five shekels in the gemara in bekorot. Rav Ahi sen17 zuz for pidion haben and Rav Acha told him to raise it to 20]