Rashi: It is an expression of a count, like "v'Sochen Levenim Titenu" (Shemos 5:18). These are the same amount, i.e. a 10th of a Chomer, just Eifah is used to measure dry goods, and Bas for liquids.

Rashi: It is 30 Sa'im. Malbim ? it is for dry things and liquids.

Rashi, Targum Yonasan: It is to take.

Radak: One who must give a tithe of a Chomer of oil or wine, he gives a Bas. "Va'Asiris ha'Chomer ha'Eifah" teaches similarly about Ma'aser of grain or other Zera'im.

Malbim (Bi'ur ha'Milos): Ma'aser is the tithe separated. Asiris is the number (amount). They would separate a [small] Bas from a Chomer (refer to 45:14:1:3), but they would not separate [a whole] Eifah ? the Nasi's portion was only a sixth of an Eifah from a Chomer of wheat or barley.

Rashi: The calculation of [the size of] the Bas and Eifah will be according to the size of a Chomer. If they will increase [or decrease] the size of a Chomer, we increase or decrease] the size of the Bas [and Eifah], so it will be a 10th.