The Shaffer Come-Along Hand Power Unit.

The unit takes up a link of chain at a time.
The handle brougt forward or back, tightens the chain.
Continuous action either way the handle is operated tightens the chain.
One or two pawls are always engaged.

To reverse the come-along alternate lifting the pawl
not under pressure while applying preasure to the handle.
Let the loose pawl slide over the reversing link.
Repeat this operation until the chain is free of tension.