THE humble zipper has become the SNP's latest inspiration for choosing its candidates for the Scottish Parliament, writes Ken Smith.

While the pedants of constitutional reform talk about single transferable votes, additional member systems, and OMOV, the Nationalists will decide this weekend whether to ''zip'' their candidates. The term refers to the neat mechanical way that the teeth of a zip mesh together when it is closed.

As voters will increasingly realise before the Scottish Parliament elections, they will actually have two votes - one for the normal constituency candidates, and one for a particular party's list of additional candidates.

The second vote is to allow for a certain amount of proportionality to come into the equation.

In order to increase the chances of a fairer balance of men and women being elected, the SNP will decide at its annual conference whether the candidates on the lists should alternate, male, female, male, female and so on down the list.

That is where the term zipping comes from.

The higher up the party list, the better chance you have of being elected, so by alternating the gender, there is a greater deal of balance.