---
name: earned-value-s-curve
description: Earned value management for a construction project - build the planned value curve from a cost-loaded schedule or payment certificates, compute CV, SV, CPI, SPI, earned schedule SPI(t), EAC/ETC/VAC/TCPI, draw the S-curve and explain in plain words what the numbers say and how reliable they are. Use when the user asks for an S-curve, "curva S", earned value, "valor ganado", "avance físico vs financiero", cost and schedule performance, forecast at completion, or a monthly progress report for the owner or the bank.
---

# Earned value and S-curve

## Inputs
- Baseline: planned value per period (from a cost-loaded schedule, the budget spread by activity dates, or the payment schedule). BAC if it differs from the last PV.
- Progress: earned value per period = budgeted value of the work actually done (measured quantities x budget unit prices, or weighted milestones).
- Actual cost per period from accounting (same cut-off date, same scope, same currency, with or without VAT consistently).

## Procedure
1. Agree the cut-off date and the progress method with the user (measured units, weighted milestones, 0/50/100, % estimated). Write it in the report.
2. If PV is not ready, build it: spread each activity's budget across its planned dates (linear unless the user says otherwise) and accumulate.
3. If EV comes from measured quantities, compute it per item: measured qty x budget unit price. Never use the contractor's billed amounts as EV without saying so.
4. Write `evm.csv` with `period,pv,ev,ac` (cumulative; or per period with `--incremental`) and run `python scripts/evm.py evm.csv --currency COP` (`--bac` to override).
5. Explain the result in 5-8 lines: cost efficiency, schedule position in time (SPI(t), forecast duration), the three EACs as a range, TCPI and whether it is realistic (a TCPI above about 1.1 usually means the budget target needs a decision, not hope).
6. Point to the drivers: which work packages contribute most to CV and SV (repeat the calculation per package if data allows).

## Output
- `evm.md` (indicators, period table), `s_curve.png`, and the plain-language reading.

## Never
- Never mix cut-off dates or scopes between PV, EV and AC.
- Never present SPI near 1.0 late in the project as "on time"; check SPI(t).
- Never invent actual costs or progress; missing periods stay empty.