What is Code of Accounts?
The code of accounts is the numbering system that uniquely identifies every WBS element (1.2.3 = project 1, deliverable 2, work package 3), letting scope, estimates, budgets, and actuals all reference the same structure. It's what lets the cost system and the schedule agree about what "3.4.2" means.
Unglamorous and essential: without it, cost roll-ups and earned value are guesswork wearing decimals.
Worked example
A contractor codes the hospital job: 03 concrete, 03.30 cast-in-place, 03.30.10 foundations. Every timesheet, invoice, and estimate line carries a code — so when the PM asks "what have foundations actually cost?", the answer is a query, not an archaeology project across three spreadsheets that each invented their own names.