A system for monitoring tissue pH calculates and displays integrated pH values over one or more user-selectable integration time periods. The values can be displayed in a numerical and/or graphical format. In the graphical format, measured values of pH are displayed as curves. A cursor can be positioned along the curves to display an instantaneous measured value at any point. The integration periods are highlighted relative to the curves. If the cursor is positioned within a region corresponding to an integration period, the display indicates the integrated value of pH from the start of that integration period to the time corresponding to the position of the cursor.