A method is disclosed to determine and assess chamber inconsistency in a multi-chambered tool, especially a multi-chambered tool involved in mass production processes. Wafers produced by the tool are grouped in lots measured to obtain loss yield groups. The invention sorts yield losses to obtain a corresponding monotonic sequence. The invention then averages the monotonic sequences. If the resulting mean monotonic sequence fits with a predetermined aberration, the tool is determined to suffer from chamber inconsistency.