Scottish independence: Donside's litmus test for SNP majority
14 May 2013 Last updated at 11:08 BST
Voters in Aberdeen Donside will vote on the 20 June to elect a successor to the late Brian Adam, the SNP MSP who died in April.
Mr Adam had a majority of 7,175 at the last election.
If Labour claim the seat, it would deprive the SNP of their majority at Holyrood.
BBC Sunday Politics Scotland's Niall O'Gallagher has been looking at the numbers.