The cross-sectional area of one limb of a U-tube manometer [ Figure shown below ] is made $$500$$ time larger than the other, so that the pressure difference between the two limbs can be determined by measuring $$'h'$$ on one limb of the manometer. The percentage error involved is :

A circular plate $$1$$ $$m$$ in diameter is submerged vertically in water such that its upper edge is $$8m$$ below the free surface of water. The total hydrostatic pressure force on one side of plate is :