Pocket coin scales, c.1820
NatWest Group History 100 object 26: pocket scales for weighing sovereigns, c.1820.
These scales were made to allow their owner to check that the coins he handled weren't just as good as gold; they were gold - and the right amount of it, too.
In the 19th century, when coins still contained a significant proportion of real gold, this was a serious business. Knowing that coins were truly worth their face value was important for everyone, but perhaps especially for bankers. Money was everyone's currency, but for bankers, it was also their main commodity. They had to be sure that neither they nor their customers were dealing in damaged or counterfeit coins, not only for the sake of avoiding financial loss, but to maintain trust.
By the early 19th century Britain's money circulation system was in disarray
Gold coins in circulation were vulnerable. Gold is a soft metal, and coins would eventually wear down as they passed through successive pockets and hands. Coin clipping was also rife. Criminals would shave away tiny amounts of gold, leaving the coin looking whole, but very slightly lighter. Collecting up the shavings would eventually add up to a worthwhile amount of gold, but the value of the official coins in circulation was gradually eroded.
By the early 19th century Britain's money circulation system was in disarray, buffeted by the financial turmoil of the Napoleonic wars. The Coin Act, passed by the British parliament in 1816 and popularly known as the Great Re-coinage, was an attempt at solving the problems with a clean sweep. The range of coins in circulation was standardised and the precious-metal content of each one fixed by law. Any coin that did not weigh the defined amount was declared unfit for circulation.
The gold sovereign, worth 20 shillings, was introduced as part of the Great Re-coinage, as a replacement for the older guinea, which had been worth 21 shillings. Sovereign scales began being offered for sale almost immediately. A portable design like this one was invaluable, because money itself is portable; that's what makes it so useful. These scales could easily go wherever a transaction might occur.
On the other hand, this particular set of scales doesn't seem to have gone very far at all. Originally sold at 33 St Andrew Square, Edinburgh, they were found in the 1990s by archivists in the bank's head office, three doors away at 36 St Andrew Square.