Program in C++ using type-safe class representations of numerical quantities without concern for the internal units or representation. Use a conventional compiler to verify dimensional integrity of computations at compile time. Add, subtract, multiply, divide, and compare quantities?but only using allowed, meaningful operators and functions. Define new units, classes, functions, .... The Quanti-D Library comprises more than 80 C++ classes representing quantitative properties (or dimensions). These include period (of time), velocity, acceleration, distance (length), area, volume, mass, density, pressure, energy, power, magnetic field, voltage, current, resistance, capacitance, inductance, luminosity, viscosity, decibels, solid angle, monetary worth, musical pitch, and many others. These type-safe classes include more than 300 standard and traditional units of measurement plus all metric system scaling prefixes. A quantity of a particular property (that is, an object of a class) has no additional memory or run-time overhead beyond that of a native floating point number. However, the quantities are type-safe, enhance self-documentation, hide the implementation and internal units, and provide unit conversion when needed.