a Lubavitcher Hasid and major posek (halachic authority) active during the first half of twentieth century. He is most famous for his works Ketzos ha-Shulchan, Piskei HaSiddur, Shi'urei Mikveh, and Shi'urei Torah (Measurements of the Torah), in the last work, he converted biblical measurements into contemporary measurements. The work is of great practical significance since much of Halacha involves specific requirements of precise sizes and quantities.