Inspired by previous experience in freeform metrology practice and industrial needs, the Czech Metrology Institute developed the freeform standard Hyperbolic paraboloid 300 of dimensions 300mm×300mm×160mm with a freeform functional area of approximately 64000mm2. The paper presents a mathematical–metrological approach to finding a suitable strategy for calibrating the freeform standard on a coordinate measuring machine with a tactile probing system. The calibration strategy consists in the development of a freeform digital twin of the standard, i.e. a continuous digital representation of a freeform measured value with associated uncertainty. A procedure to estimate the uncertainty of the coordinate freeform measurement is described, too. After calibration, the Hyperbolic paraboloid 300 standard will become a verification gauge suitable for use as a precision reference in advanced freeform metrology similar to common verification gauges widely used in length metrology.