The article discusses the optimal amount of money that should be in circulation to maximize economic efficiency. The researchers developed a model to calculate the best inflation tax, showing that the Friedman rule may not always be the best approach. They found that taxing money is usually best when there are economies of scale in money demand or when money is needed for taxes. Additionally, heavier taxation of money is recommended when the demand for money is not very sensitive to changes in interest rates. Empirical evidence suggests that an optimal nominal interest rate is less than 1% per year.