Abstract: A method and apparatus for generating a bill image in a computer implemented billing system for a telecommunications network which includes providing a plurality of discounts for a customer retroactively applied to calls made during a billing period in which the discounts apply. The method includes loading qualification criteria for the plurality of discounts and customer account details into the billing system, generating a data structure defining a time line over at least part of which the discounts are operative, the time line being divided in dependence on the qualification criteria and customer account details into a number of segments each of which corresponds to a period during which a respective version of the discounts were operative, accumulating charges for the calls made during each segment, and calculating the appropriate discounts from the accumulated charges for each segment for calls which qualify for the discounts.

Abstract: An air cleaner for removing air entrained cooling oil mist, smoke and particulates which become air borne during machine tool cutting operations and the like thereby contaminating ambient air adjacent the machining and the like operations.The contaminated air is driven against a planar impingement plate arranged to be struck with a glancing blow of such force as to remove a substantial portion of the contaminates by impact.A series of cylindrical openings extend transversely through the impingement plate. The openings are sufficient in number to ensure continued flow through the cleaner. The plate is arranged at such an angle with respect to the air flow directed toward the plate that the openings appear to be elliptical to the air stream when the air first strikes the plate, thus effectively increasing the impingement surface area, but at the same time an adequate number of openings is provided through the impingement plate to maintained the desired air flow.