The Roberval Balance is a weighing scale invented by Gilles de Roberval. In this scale, two identical horizontal beams are attached, one directly above the other, to a vertical column, which is attached to a stable base. On each side, both beams are attached to a vertical beam - at the same distance they are attached to the vertical column. The two identical vertical beams are attached at the top to two identical horizontal plates, suitable for placing objects to be weighed. An arrow and a ruler on the lower horizontal beam and vertical column (respectively) may be added to aid in seeing level. The object to be weighed is placed on one plate, and calibrated masses (of various masses) are added to and subtracted from the other plate until level is reached. The mass of the object is equal to the mass of the masses - regardless of where on the plates items are placed. This is simple to understand by ignoring the torque placed by an off-center mass on the vertical beam beneath it. Instead understand that the scale design requires the vertical beams to remain vertical, even when one is higher than the other. Since the beam is vertical, the off-center mass can only practically exert a wholly downwards force (vertical vector with no horizontal vector). The Roberval Balance is arguably less accurate and more difficult to manufacture than a beam balance with suspended plates. The suspended-mass balance, however, has the disadvantage of having strings in the way. The Roberval Balance, therefore, has, for over three hundred years, been very popular for applications where convenience and moderate accuracy are required, notably in retail trade.

External links

• The Roberval Balance