As part of his description of how Jews face Jerusalem when we pray, Rabbi Steinsaltz writes:
“Rabbi Schneur Zalman of Lyady writes in his halakhic work, known as Shulhan Arukh ha-Rav, that in order to establish the exact direction it is necessary to use spheric trigonometry.”
--Rabbi Adin Steinsaltz
From A Guide to Jewish Prayer, p. 291, by Rabbi Adin Steinsaltz
