Wright's own 1936 formula is a power law of cumulative production quantity, log-log linear — not a function of calendar time

economicswrights-lawlearning-curvetp-wright-1936cost-curvesprimary-source-verification

Wright's own paper states that in developing a curve of labor cost against production quantity, "it became evident" the relationship fit a formula of the form cost-factor = (quantity)^exponent, with the exponent solved from the ratio of logarithms, and that "when plotted on log-log paper, it becomes a straight line." His Fig. 3 — "there called the eighty percent curve" — carries an exponent of .322. This is the structural core of Wright's Law: cost as a straight line in log-log space against cumulative quantity produced, not against elapsed time.

Both restatements checked against this primary agree with it on exactly this point. Our World in Data explicitly draws the same production-vs-time contrast the primary implies: "we looked at price changes not as a function of time, but of experience." New Things Under the Sun states the learning curve "asserts that every doubling of total experience leads to a consistent decline in per-unit production costs" — experience (cumulative output), not calendar time, again. This production-not-time framing is also the precondition behind Sahal's identity: Wright's Law and Moore's Law collapse into the same curve only when cumulative production happens to grow exponentially in calendar time, which is a fact about the world, not a fact built into either curve's definition — and Wright's own 1936 text confirms which axis his curve was actually defined against.

On this specific structural point, the modern one-line summary of Wright's Law is not a drift from the original: it is the original.