Voters are given a ballot paper which asks them to record two (‘X’) votes. The first vote is for an area or constituency MSP. In the constituency vote the person with the most votes wins. There are 73 constituency MSPs.
Under AMS voters are also given the opportunity (a second vote) to vote for a political party. Once all the first votes are counted and constituency MSPs elected, this second vote is used to make the overall representation of each of the political parties fair.
After all the constituency votes are counted, additional MSPs are allocated to each of eight Scottish parliamentary regions to make the overall result fairer to all parties.
For example, in 2011 the Conservative Party were given two additional (or list) MSPs in the North East Scotland region as they failed to return any constituency MSPs. This gives Conservative Party voters fair representation in proportion to their political support in the North East of Scotland.
There are 56 additional regional MSPs (7 per region). When added to the 73 constituency MSPs this makes 129 MSPs altogether.