Target referred for convergence measurements and the same tunnel

摘要

Has a mount (2) which is engaged by force into an opening of the same shape formed in a support(1). This support(1) is designed to be sealed in the tunnel wall. The mount is fixed to two paper reflecting discs(21) arranged opposite to each other. The centre of the two reflecting disc has a hole(22) for insertion of an extension piece which can also be fitted with a target.