GPO parcel scale by De Grave, London with 6 Imperial and 8 metric weights

Roberval type balance used by the General Post Office for weighing parcels and made by De Grave, London. This balance was supplied with both metric (kilogram) and Imperial (pound) weights. This type of equal-arm platform scales uses linkages connected under each pan and joined together under the beam. Forming a parallelogram they utilize the Roberval principle that allows the pans to rest above the balance pivot rather than hang underneath the beam, as is normally the case in an equal-arm balance.