Various kinds of control performance index have been studied widely during the last decade. In this paper a set of performance indices appropriate to level control is chosen and a fast, simple, online method is presented for monitoring the control loops. A graphical, user-friendly and interpretable display for operators to display performance indices has been developed that can be easily implemented for any control system. This tool can be used for statistical monitoring of control loops, predictive maintenance, fault diagnosis, and for tuning the controllers. Tests were performed with a pilot flotation cell, and the results are presented and discussed in this paper.