down, and ensures that the smaller a constituency is, the more strictly proportional its parliamentary representation will be. Another set of rules apportions the 50 seat premium for the largest-tallying party among constituencies. Individual seats are apportioned by "cross of preference". Voters mark a cross next to the name of the candidate or candidates they prefer, the number of crosses varying from one to five depending on constituency size. Ballots with no crosses or more crosses than allowed, count for only the party but not the individual candidates. Tallying is done manually in the presence of representatives of all contesting parties. Party tallying, which is easier, is done first so that returns may be announced quickly. Individual candidate tallying is done next and can take several days. Once the number of seats per party and constituency is determined, the seats are filled on a top-down basis from the individual cross-of-preference tallies. Party heads and acting or past Prime Ministers are exempt from cross-of-preference voting: they are automatically placed at the top of their party list and are elected, provided their party achieves at least one seat in the particular constituency. By constitutional provision, the electoral law can be changed by simple parliamentary majority, but a law so changed comes into effect in the next-but-one election, unless a two-thirds parliamentary supermajority (200 or more votes) is achieved. Only in the latter case is the new electoral law effective at the next election. A case in point is the current electoral law, which was passed in 2020. Because this law was passed by a simple majority, it will not used for the subsequent 2023 election, but can be used in the 2027 election. Electorate All Greek citizens aged 17 or over in the year of the election are eligible to vote, provided they are on the electoral register, unless: they are imprisoned for a criminal offence and they have been expressly deprived of the right to vote by judicial decision (this happens only in the rare cases of high treason or mutiny). Incarcerated persons vote in polling stations specially set up inside prisons they are mentally incapable of making a reasoned judgement, according to a judicial decision. In practice, this applies only to a percentage of institutionalised mental patients According to Presidential Decree 26/2012(as amended by law 4648/2019), article 4, the 1st of January is-for electoral purposes-considered the birthday of all citizens