This paper deals with the determination of uncertainty and individual contributions to the measurement uncertainty on the CMM SIOS NNM-1 instrument fitted with the touch-probe scanning system Gannen XP. Manufacturer SIOS designates this machine as nano-CMM. Two non-simulation methods to determine the measurement uncertainty, the substitution and multi-position methods are addressed in detail [Sramek, Jankovych 2018]. Ruby balls with various nominal diameters are used as the measured objects. One simulation method to determine the measurement uncertainty, the Monte Carlo method, is also addressed in this paper. The paper also summarizes and specifies calculation methods to determine the measurement uncertainty, and provides results of representative sets of measurements, including determination of the expanded measurement uncertainty. This paper contains novel conclusions in the area of uncertainty measurement of nano-CMMs.