Under the Scotland Act 1998, ordinary general elections for the Scottish Parliament are held on the first Thursday in May every four years (1999, 2003, 2007 and so on). The date of the poll may be varied by up to one month either way by the Monarch on the proposal of the Presiding Officer. If the Parliament itself resolves that it should be dissolved (with at least two-thirds of the Members voting in favour), or if the Parliament fails to nominate one of its members to be First Minister within 28 days of a General Election or of the position becoming vacant, the Presiding Officer proposes a date for an extraordinary general election and the Parliament is dissolved by the Queen by royal proclamation. Extraordinary general elections are in addition to ordinary general elections, unless held less than six months before the due date of an ordinary general election, in which case they supplant it. The following ordinary election reverts to the first Thursday in May, a multiple of four years after 1999 (i.e., 5 May 2011, 7 May 2015, etc.).