PE (or PER) is a valuation ratio of a company's current share price compared to its per-share earnings.

PE = Last Close Price / Earnings Per Share (e)
Factset does not restate estimates which can vary from one analyst to another, because of the different methodologies on what should be included in earnings and what should be considered as the appropriate number of shares to calculate the EPS.
Once a company has disclosed its financial statements for a given fiscal year, differences may remain between analysts' estimates and reported figures, due to the different methodologies; this is the reason for which Factset's data is still considered as being a consensus.
Consensus estimates calculated by FactSet are based on estimates that have been validated via broker research within the past 100 days.

PE relates the current share price with the market expectations in terms of Earnings Per Share (EPS). For example, if current share price is US$ 75 and expected EPS for 2007 is US$ 12, PE for 2007 is 6,25.
PE widely varies from one company to another. Nevertheless, companies operating in the same business tend to have closer ratios, particularly when they show similar growth expectations.
When comparing companies using their PE, it is also necessary to compare their Trading Multiples (particularly EV/EBITDA), because unlike PE, they take into account and level up for each company's capital structure: the PE ratio relates to the equity value whereas Trading Multiples relates to the Enterprise Value.