BT BQ 61a(20) :
See the entire entry for barrāy adj. exterior

BT BQ 61a(20) :תנא דידן קא חשיב מלעלה למטה תנא ברא קא חשיב מלמטה למעלה‏ : our (i.e., mishnah) tanna is calculating it from top to bottom, while the barraita tanna is calculating it from bottom to top
See the entire entry for ḥšb vb. to think, calculate