The number of outstanding shares can change due to the issuance of new shares, repurchase of existing shares, or conversion of employee options into shares. Companies may also issue shares in multiple classes, which may not be of equivalent value. For example, Berkshire Hathaway has two publicly traded share classes: BRK.A and BRK.B. The weighted average shares outstanding is a calculation that accounts for any changes in the number of outstanding shares over a specific reporting period.