Investment analysts might sometimes not have understood "beta" as Sharpe had intended. They often took beta to be a direct measure of a stock's individual riskiness rather than a measure of a stock's covariance with the overall market, and thus of the stock's contribution to the overall risk of a diversified portfolio. Nevertheless, "beta" became a lasting feature of how sophisticated practitioners talked, and still talk, about financial markets.

Donald MacKenzie, An Engine, Not a Camera, loc. 1129