Showback: early maturity, transparency first; Chargeback: when usage is measurable and the organization supports internal billing; adopt unit rates ("bill of IT") and SLAs. TBM exemplars document vendor invoice normalization to ATUM taxonomies for clean showback/chargeback.
How do we set unit rates?
Unit rate = (Total allocatable cost for a service ÷ consumption units), with rider charges for shared/unallocated pools and commitment credits (e.g., reserved instances). Publish a rate card and true‑up quarterly.
