225 ILCS 470/3: Recognition and use of systems.

The system of weights and measures in customary use in the United States and the metric system of weights and measures are jointly recognized, and one or the other of these systems shall be used for all commercial purposes in this State. The definitions of basic units of weight and measure, the tables of weight and measure, and weights and measures equivalents, as published by the National Institute of Standards and Technology, are recognized and shall govern weighing and measuring equipment and transactions in this State.