Alignment of the low-$\beta$ magnets and the experiments in the LHC

For the LHC project the demands on alignment and positioning have been increased with respect to previous projects; this concerns the experiments as well as the accelerator. Alignment and continuous monitoring of the low-beta magnets in combination with new methods have become necessary. The layout of the measurement system provides a permanent follow up of the magnets, the possibility of remote alignment and has interfaces to the alignment reference network in the experimental area. The low-beta magnets define the Nominal Beam Line which is the reference for the experiments. The installation of the experiments started up to five years before the low-beta magnets arrived in the tunnel. The influence of deformation on the cavern had to be taken into account. This problem had to be considered for assembly and positioning work of the numerous detector parts.