Clinic QRS recently billed Henry directly for his cosmetic rhinoplasty $($nose reconstruction$).$ This was performed by QRS$\text{'}$s Plastic and Reconstructive Surgery Department.$$

Henry's bill was based on the following cost$-$apportionment steps:$1)$ a one$-$time allocation of costs between the non$-$revenue departments that serviced each other for Henry's rhinoplasty $($Facilities and Medical Imaging$)$;$2)$ simultaneously, a one$-$time allocation of costs between the revenue departments that also did work for each other relative to Henry's rhinoplasty $($i$.$e$.,$ Plastic and Reconstructive Surgery and Anesthesiology$)$; and after #$1$ and #$2$ were completed, $3)$ a one$-$time allocation of the individual costs$/$expenses of Facilities and Medical Imaging to the Plastic and Reconstructive Surgery Department, out of which Henry's hospital bill was finally issued by Clinic QRS$.$

The apportionment method adopted for Hnery's surgery invoice is known as $\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.$