In the case of voting by show of hands, the President of the House presumes that the MPs who are present, are voting on behalf of their entire parliamentary group. Every MP, however, has the right to request that the vote be taken by roll-call, which means that all MPs present have to cast their votes individually by saying "for" or "against". In a roll-call vote, members of the same political group may vote differently.
Every vote matters
Because every vote matters, it is important that as many MPs as possible attend the plenary sitting for voting. That is why the President of the House rings a bell that can be heard throughout the building before the voting begins. The items to be voted on are tabled on the voting list, which is published in advance. Voting is by secret ballot only in the case of nominations or appointments, for example the election of the President of the House.