In order to receive money from the Commission, organisations must produce reports and costs showing that the costs claimed are related to the project. In order to claim personnel costs, organisations have to show that staff were working on a specific project. The way to show this is by keeping some sort of time recording mechanism (possibly even at a task level).
The Finance Helpdesk has produced a leaflet with Guidelines on how to correctly record personnel costs within FP7 projects.
To view the leaflet click here.