Poundal (pdl)

The imperial unit of force, being that which accelerates a mass of one pound at one foot per second squared.

British engineers working before metrication needed a coherent force unit within the foot-pound-second system, and the poundal supplied it. Its awkwardness is instructive: because the pound was already doing service as both a mass and a force in everyday speech, the poundal existed largely to disentangle the two for calculation. It has been almost entirely displaced by the newton, but it appears throughout British engineering texts of the nineteenth and early twentieth centuries, and anyone reading period ballistics or structural work will meet it.