European Community (EU) introduced two confusing and ambiguous concepts: [http://europa.eu.int/scadplus/leg/en/cig/g4000q.htm 'Qualified Majority Voting'] and 'Council'
The Council of Ministers is the prime policy-making and legislative body 
of the European Union. It comprises the Ministers of all  Member States.
It  meets in various forms (e.g. the Environment Council, the Economic and 
Finance  Council) .  The 'European Council'  is composed of heads of member states
plus two or three EU officials.  

Council likes to make decisions by consensus, respecting the veto of the the states, as many states consider some of 52 identified areas (such a social policy , tax matters, immigration and asylum affair, transport ..) to be the within the 'red lines' , to be so essential that the states do not want to be compelled by any majority. As number of member states is increasing, there is need to move from veto power to some form of majority vote, hence QMV.

Treaty_of_Nice   defined three forms of QMV valid for two scenarios.

For council, at least in one of its forms, it assigned

  • To the large states, (UK, France, Germany )
percentage of votes which is less then percentage of their population.

  • To small states, ( Luxembourg, Malta, Slovakia, ..) percentage of votes
larger then the percentage of their population.

  • The medium size states (Poland, Spain) number of votes proportional to
their population.

QVM required that threshold of such weighted 'votes' was reached.

This 'regressive weighing of the votes' would be valid until year 2009. It was not clear how it could be changed, by unanimity, or by some QMV.

The draft constitution, 'article 24', proposed that 'qualified majority' shall consist of two thirds of the Member States, representing at least three fifths of the population of the Union.

By that, the proportionality, rather then regressive weighing, would be used.

Some, particularly middle sized, states, were afraid that with such double-majority system EU would be governed by the four most populous states.

No solution was reached in 2003 and meeting in December ended in failure.

Draft is also ambiguous on the voting in Parlament: Article 19: The European Parliament Chapter I - The institutional framework says

2. The European Parliament shall be elected by direct universal suffrage of European citizens in free and secret ballot for a term of five years. Its members shall not exceed seven hundred and thirty-six in number. Representation of European citizens shall be degressively proportional, with a minimum threshold of four members per Member State.

But does not defines ther term 'degressively' (regressive weights) nor a method of defining or changing it.

One wonders how USA can function with just two clearly defined legislative bodies, congress and the senate, each with simple voting rules. Passing a bill in congress and senate corresponds to the EUs double majority - but process description is less convoluted.