The "Introduction" to his options service that Black circulated gave simple instructions how to identify and to exploit opportunities for spreading (Black 1975b, p. 7). Spreading avoided both the difficulties of the more basic BlackScholes arbitrage strategy described above. It was "less sensitive to the estimated volatility of the stock" because "an increase in the volatility estimate will increase the value of all the options on a stock" (Black 1975a, p. 40), and it did not require purchases or sales of stock: it required only purchases and sales of options.

Donald MacKenzie, An Engine, Not a Camera, loc. 734