Yale N. Patt and Sanjay J. Patel, Introduction to Computing Systems: From Bits and Gates to C and Beyond Second edition, McGraw-Hill Higher Education, Boston (2004) ISBN 0-07-121503-4 Softcover, pp 632, plus XXIV

An improved access tower for use in the manufacture of tunnel modules and tunnel sections for building underwater tunnel tubes is provided. The tower is positioned at one end of the tunnel module shells when they are placed on pedestals for rotation and further processing. Assembly of the support framework around the shell is conducted from the top position on the shells. A moveable bridge extends from the tower for access to the top of the shell.