Since you do not know how the fair value is defined, so, let me tell you what my understanding of fair value !!
The market is dynamic, and it is chaned every second, the market is made of the true value of the company which is calculated with PE, cash flow, revenus, ...etc, and that is the "current" value which is already realized, however, since the market involves humanbeings, and the prospect of every product , and future prospect revenue and profit , the expectation , is changed every second, as a result, the fair value , the value which has realized + the future value is changed every minute, as a result , the share price is changing every second after the market is open. Example, after the job data was released this morning, CENX went up immediately, that is because people expect the recovery is solid, and CENX's future will be improved quarter after quarter as economy continue to improve, as a result, the expectation of revenue and profit of the the next few quarters is increased and as a resut, the share price reflect that expectation. All in All, the fair value is the current value which has been realized plus the future value which is expected to be realized, and the fair value is dynamic, changed second by second,all in all, the fair value is the price of share the last trader is willing to pay !!!!!