HOW DO YOU WIN A GENERAL ELECTION?
The simple answer is by winning more seats in the House of Commons than all the other parties put together. At the moment there are 646 seats up for grabs, which means 324 seats are needed to win an overall majority.
HAS PARLIAMENT SHRUNK?
Yes: In the 2001 election there were 659 seats in the Commons, this time there are 646. This is because Scotland has seen its number of seats reduced by 13, from 72 to 59. This is so Scottish constituencies are now the same size, in terms of population, as those in England.
WILL SCOTLAND'S BOUNDARY CHANGES AFFECT THE RESULTS?
Detailed research has been conducted to allow comparisons between the 2001 and 2005 elections, taking into account the different numbers of seats in the House of Commons now and then.
In 2001 the UK-wide results for the main parties now affected by boundary changes in Scotland were: Labour 413 seats; Conservative 166; Liberal Democrat 52; SNP five.
The research concluded that had the boundary changes been in force in 2001 the results - known as "notional" results - would have been: Labour 403; Conservative 165; Liberal Democrats 51; SNP four.
The BBC uses these notional results as the basis for its calculations of each party's gains and losses on 5 May.
HOW DO BY-ELECTIONS FIT IN?
For the purposes of tallying up the results and allowing a straightforward comparison with previous general elections, all by-elections - held in individual seats between general elections when an MP steps down or dies - are ignored.
For example, Labour won the London seat of Brent East at the 2001 general election but lost it to the Liberal Democrats in a September 2003 by-election. If Labour were to win this seat back at the general election on 5 May, the BBC will describe it as a Labour "hold", not a Labour "gain".
Defections of MPs from one party to another are treated in the same way.
WHAT HAPPENS IN THE SPEAKER'S SEAT?
The Speaker of the House of Commons is an MP and has to stand for re-election in his or her constituency at every general election. Traditionally the biggest parties in the House of Commons do not stand against the Speaker, although other parties do.
The current Speaker, Michael Martin, is standing for election in Glasgow North East. The Speaker is a neutral figure in Parliament, so Mr Martin is no longer a member of the Labour Party as he was before his election to the role (by all the other MPs).
However, should he be re-elected, for the purposes of calculating the number of seats belonging to each party his will be included in Labour's total.
WHAT IS A HUNG PARLIAMENT?
A hung Parliament happens when no single party wins a majority over all the others. One likely result of this happening is a minority government taking office, when the monarch - advised by experts - chooses the leader of a party to form a government. Alternatively, a coalition government can be formed, when two or more parties use their combined numbers to create an overall majority.
The last time a hung Parliament happened in the UK was in February 1974. Labour Prime Minister Harold Wilson led a minority government, after taking just four more seats than his Conservative rival Edward Heath.
WHAT IS SWING?
Swing is a tool which helps explain how elections are won and lost. It simple terms it is a way of measuring how the public's support of political parties changes from one election to the next.
Although it gives an apparently clear picture, the disadvantage of swing is that it can only tell you about a shift from one party to another, not the shift between three or more parties.
Swing is calculated by taking the average of one party's fall in the share of the vote and another party's gain in support.
For example, in the last election, the swing across the UK, excluding Northern Ireland, was 1.8% from Labour to the Conservatives.
This was calculated by adding the 1.2% increase in the Tory share of the vote and the 2.4% drop in Labour's share and dividing by two.
WHAT IS AN EXIT POLL?
An exit poll differs from an opinion poll in two main respects. Firstly it is conducted on election day, and secondly it is a survey asking people who they voted for after going to the polls, rather than who they intend to vote for ahead of time.
The results of this year's exit poll will be broadcast just after the polls close at 2200 BST, 5 May.
The BBC and ITV jointly commissioned NOP and MORI to undertake the fieldwork.
Thousands of voters will be questioned in marginal seats, to create a prediction of the election's result.
Further predictions will be made on election night, in addition to the exit poll. Once the first constituencies begin to declare, the figures they provide can be used to create a results based forecast which will be updated as more results follow.
IS ONE SEAT MISSING?
Due to the death of Jo Harrison, the Liberal Democrat candidate for Staffordshire South, no election will take place there on 5 May.
This means that the election result will be made up of a total of 645 seats, not 646.
A by-election will be called in Staffordshire South after the general election has taken place, although it is not a by-election in the traditional sense of one being caused by the death of a sitting MP.