A method for measuring soil in a wash liquor or other soil-containing liquid medium, the method comprising: a) a soil sensing step wherein the soil-containing liquid medium is contacted with a plurality of fuzzy-correlated soil-sensing means, each responsive to a distinct physico-chemical soil characteristic and providing one or more soil parameter measurements corresponding thereto; b) a data processing step wherein the soil parameter measurements for each sensing means are entered as input data into a model algorithm defined on the basis of an algorithm dataset comprising experimental or consumer-generated soil parameter and soil concentration information and which functions to generate predicted soil data of enhanced confidence level; and c) a communication step wherein one or more signals dependent upon the predicted soil data is issued to an output device, data store, user interface, data processor, or an appliance director or module. The invention also relates to methods for measuring the degree of soiling of a soiled article, and methods for cleaning a soiled article in a wash liquor or other liquid medium.