National accounts were designed in the 1930s and 1940s to answer a specific question: how much could an economy produce for a war effort. They measure the value of output exchanged for money, which was a reasonable proxy for economic activity in an economy of factories and farms. Applied to an economy where a growing share of value is unpriced — software distributed free, care provided within households, the cost of environmental damage — the same measure omits more than it once did. Economists have known this since the accounts were built. What has kept the measure central is not that anyone believes it captures welfare, but that the alternatives are harder to compile and easier to manipulate.