This invention relates to a vacuum processing apparatus having vacuum processing chambers the insides of which must be dry cleaned, and to a method of operating such an apparatus. The formation of the looped zipper segment causes the package to have a wide open mouth, and a natural tendency toward the open configuration. Diagnostic circuitry compares processed outputs from at least two subsections of the infrared image and provides a diagnostic output based upon the comparison. A compressed sequence of tokens is generated from the compressed cluster sequences of tokens. The system triggers an event in response to the detected aberrance.