Many of the important decisions involve just one or two of the subsystems. The pros and cons are initially discussed in the subsystem plenary meetings. The term "plenary" here implies that all collaborators working within the specified group (for example the subsystem) can participate in the meeting and make their voices heard. Recommendations are then discussed in the ATLAS Executive Board, and presented in ATLAS plenary meetings which play a primary role in forming a large consensus about issues for which decisions are required. The leadership can only 'lead' the collaboration to decisions which are understandable to all, or at least to a large majority. Practical constraints may influence decisions, like costs, schedule, the availability of teams to take responsibilities for the execution... Procedurally there is a clear sequence of steps to formally make decisions, with a hierarchical structure from sub-system to systems, and ultimately with the vote in the Collaboration Board being the final step for very major decisions.

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