XVI - XVII. Currency union and weights and measures
XVI. THAT from and after the Union, the Coin shall be of the same Standard and Value throughout the United Kingdom, as now in England, and a Mint shall be continued in Scotland; under the same Rules as the Mint in England, and the present Officers of the Mint continued, subject to such Regulations and Alterations as Her Majesty, her Heirs or Successors, or the Parliament of Great Britain shall think fit.
XVII. THAT from and after the Union, the same Weights and Measures shall be used throughout the United Kingdom, as are now established in England, and Standards of Weights and Measures shall be kept by those Burghs in Scotland, to whom the keeping the Standards of Weights and Measures, now in Use there, does of special Right belong: All which Standards shall be sent down to such respective Burghs, from the Standards kept in the Exchequer at Westminster, subject nevertheless to such Regulations as the Parliament of Great Britain shall think fit.
A single currency was established - the English standard (which, given that it commanded 95% of the economy already, was inevitable). The rate of exchange was set according to the relative values of the English and Scottish pounds at the time: 1 pound Scots was equated to one shilling.
The natural reading of the article would be to throw out the whole system of Scottish coinage and the mint that made it, so it was also provided that Scottish mint would stay open, retasked with coining the new money.
In a similar way, a comon definition of weights and measures was established - vital in a trading economy that sold merchandise by pounds and tons and gallons, and so needed to ensure every merchant used an honest weight.