Series · 2 parts
One path through the measurement articles, in the order the ideas build: what earned value actually measures, the two indices everyone quotes, the flow metrics that replace them in iterative delivery, and what to do when the numbers say you are behind.
Three figures read at one date. Planned value is what the baseline said would be finished by now, earned value is what did finish, actual cost is what finishing it cost.
Two ratios off one earned value figure. SPI divides it by the plan and reads schedule. CPI divides it by the bill and reads cost. Below 1 is bad news in both, for different reasons.