Parallel coordinates permit large volumes of historical process data to be analysed, possibly as a precursor to the implementation of multivariable control. By changing the plot ranges, data sets which violate any of the lower or upper limits will be excluded. Including a measure of profitability as one of the parameters also permits only high profit operating conditions to be displayed. The remaining data sets can then give a clear indication of the operating strategy that will be adopted by the multivariable controller. Even without multivariable control, this tool can be useful in identifying optimum operating strategies. Data are simply imported via a spreadsheet.