First turn in LHC

The requirements on the magnetic field errors, magnet and BPM accuracy for a first turn in the LHC have been examined. The presently expected errors are satisfactory for an easy commissioning. The first turn would be less easy if both field and alignment errors are multiplied by two. The first turn becomes problematic if they are multiplied by four. The BPM accuracy measurements is not an issue as long as it is better than their alignement accuracy.