Progress in science and engineering relies on accurate and precise measurements. Flotation is no exception. It is arguable that progress in both fundamental understanding (modeling) and plant practice has been limited by the lack of instruments and sensors capable of functioning in operating flotation machines. The McGill Mineral Processing group has developed instruments and procedures to measure three variables in industrial cells: superficial gas velocity, gas-holdup and bubble size distribution. This communication describes advances on equipment and operating procedures, and introduces a protocol for sensor installation and documentation that makes possible the correction of measurements to bubble-collection-point conditions. (c) 2007 Elsevier B.V. All rights reserved.