What is a Chomer?
Rashi: A Chomer is the equivalent of a Kor, i.e. 30 Sa'im. 1
Ha'Kesav veha'Kabalah: It is proper to seed a Chomer of barley in it, i.e. it is 75,000 square Amos.
When in the Yovel cycle does the assessment of 50 Shekel per Chomer of barley apply?
Rashi: The assessment of 50 Shekel 1 per Chomer of barley applies at the beginning of the Yovel cycle, 2 which means that each year is assessed at a Shekel plus a Pundiyon 3 per Chomer. Consequently, in the event that someone comes to redeem the field from Hekdesh during the Yovel cycle, he deducts the years from the sale up to the redemption at the rate of a Sela and a Pundiyon per year, and pays the Gizbar of Hekdesh the balance. 4
The Shekel mentioned by the Torah is double the regular Shekel - which means that it is the equivalent of a Sela (Refer to 27:25:1:1)..
Rashi: This is the explanation of Pasuk 17.
Rashi: A Pundiyon equals one 48th of a Sela. See Ikar Sifsei Chachamim. Moshav Zekenim - this is like Chachamim. According to R. Yehudah, there is one less year between one Yovel and the next, so each year is a Sela and two Pundiyonim.
Rashi: This is the explanation of Pasuk 18.