The technique described is bottom-up estimating. This method involves estimating the cost or duration of individual work packages or activities at the lowest level of the Work Breakdown Structure (WBS). These detailed estimates are then aggregated or "rolled up" to derive a total estimate for the entire project. This approach is generally considered the most accurate and detailed method of estimating because it is based on a thorough understanding of the work required for each component.

1. Project Management Institute. (2017). A Guide to the Project Management Body of Knowledge (PMBOK® Guide) (6th ed.). Project Management Institute. Section 7.2.2.4, Bottom-Up Estimating, p. 244.

2. Project Management Institute. (2021). A Guide to the Project Management Body of Knowledge (PMBOK® Guide) (7th ed.). Project Management Institute. Section 4.2.3, Models, Methods, and Artifacts, p. 163.

3. Vanhoucke, M. (2012). Project Management with Dynamic Scheduling: Baseline Scheduling, Risk Analysis and Project Control. Springer. p. 35. (Describes bottom-up as a detailed estimation based on the WBS). DOI: https://doi.org/10.1007/978-3-642-25175-7