the world > the earth > earth sciences > geography > map-making > surveying > [noun] > surveying instruments > chain > trough to support (2)
Ordnance Survey. Applied to wooden troughs used to support the chain in measuring a base-line of an Ordnance Survey.
An arrangement or structure of coffers. In quots. referring to the ‘coffers’ or troughs used to support the chain in measuring the Ordnance Survey…