The tractate of Shabbos is, as its name suggests, dedicated to all the laws of Shabbos—both the creative activities forbidden on the Day of Rest as well as its various associated obligations.

The last section of the tractate discusses the prohibition of measuring on Shabbos. Though taking measurements is not included in any of the thirty-nine general categories of work forbidden on Shabbos, nevertheless it is forbidden based on the verse in Isaiah (58:13): "If you restrain your feet because of the Shabbos, from performing your affairs on My holy day... and you honor it by not doing your wonted ways, by not pursuing your affairs..." As such we abstain from all weekday-like activity, that sort that is usually performed in the course of business.

Ulla visited the home of the exilarch, where he saw Rabba bar Rav Huna on Shabbos sitting in a vat of water and measuring it.

Ulla said to him, "Though the sages did permit measuring on Shabbos in an instance where it is for the purpose of a mitzvah,1 if it is not for the purpose of a mitzvah did they allow?"

Rabba bar Rav Huna responded: "I am merely occupying myself." (Since the measurement was not for a specific purpose, it was not prohibited.)