Software for calculation with physical quantities

Software support for calculations involving physical quantities is discussed. A Python package (called Quantity-Value) is presented that allows a measured value to be paired with a measurement unit (scale), in an entity that can be used in mathematical operations. The software applies the rules of quantity calculus so that the nature of quantities, and the measurement scales, become an integral part of calculations. To overcome traditional difficulties with unit-checking systems, the software places emphasis on quantities, rather than units. Quantities of interest in the problem domain can be declared and dimensional information for 'dimensionless' quantity ratios can be retained. This approach appears to be more powerful than systems designed to work directly with measurement units.