Changes

and <math>d_2 = d_1-\sigma\sqrt{T}</math>

and <math>d_2 = d_1-\sigma\sqrt{T}</math>

This is the famous Black-Scholes formula for the price of a European call. Note that all the  variables except for <math>\sigma</math> can be observed in directly in the market. The volatility, <math>\sigma</math> of the stock must be estimated using either statistical data, or inferred from the price of options being sold in the market.

This is the famous Black-Scholes formula for the price of a European call. Note that all the  variables except for <math>\sigma</math> can be observed in directly in the market at time <math>t</math>. The volatility, <math>\sigma</math> of the stock must be estimated using either statistical data, or inferred from the price of options being sold in the market.