Kav HaYashar (The Just Measure) is a classic of Jewish musar literature, a collection of folkloric legends, moral guidance, and customs. First published in 1705 in Frankfurt, Germany, it has appeared in over 80 editions, in nearly every country around the globe with a Jewish community. The work draws on "Yesod Yosef", a musar work infused with the Kabbalistic teachings of Isaac Luria, written by Kaidanover's teacher, Yosef Yoske of Dubno.