Next time you receive a Liberal Democrat leaflet look for a graph of recent election results. And then have another look. Because it might not stand up to scrutiny.
Nick Clegg's party built its electoral success by positioning itself as the 'only alternative' to whichever party currently holds a constituency. They then try to convince Conservative supporters to vote Lib Dem in order to keep Labour out, and vice-versa.
This only works if the Lib Dems successfully convince the public that they are the only challenger in a very tight electoral race. And this often involves adopting an approach to a graph's y-axis that would result in any 16-year-old failing GCSE maths, as these examples from Liberal Democrat leaflets show: