This short video shows one of the composition casters at the Alembic Press in action during a workshop in 2008. This particular caster, serial 29472, is dated 1968, and is run by a single phase electric motor. The caster is fitted with unit shift, slow speed gearbox, and unit adding (though as yet the Alembic Press has not used the latter function).
(if no video is shown, make sure that ActiveX controls have been enabled in your browser)