HS06 stands for HEP-SPEC 2006 which is a standard across WLCG to express processing power, in the same way as Terabytes express storage capacity.
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The Gratia Project (contributed as an OSG Activity) designs and deploys robust, scalable, trustable and dependable grid accounting and auditing services, publishes an interface to the services and provides a reference implementation.

The accounting infrastructure is a complex system that involves various sensors in different regions, all publishing data to a central repository. The data is processed, summarized and displayed in the accounting portal, which acts as a common interface to the different accounting record providers and presents a homogeneous view of the data gathered and a user-friendly access to understanding resource utilization.