Front-End Engineering Design.
FEED is where the controls scope first becomes a number on a budget. The P&IDs are preliminary, the equipment list shifts weekly, and the I/O count drives PLC sizing, cabinet count, and DCS license cost before any of it is locked.
Use it through the lifecycle.
The I/O count from FEED drives the Class 3 estimate, the PLC and DCS license selection, and the marshalling cabinet count. Get that number off the actual drawing set with the BPCS and SIS scope separated, before the estimate is presented to the approval board.