The Emergency Care Research Institute (ECRI) declares dosing errors, where pumps or administration devices fail, staff unknowingly bypass a safety mechanism or the infusion is incorrectly programmed, as the greatest health risk in 2017 [6]. These errors, especially those that result in incorrect drug delivery to the patient, can harm the patient and even lead to death. A well-defined metrological infrastructure is needed to perform traceable measurements with infusion devices and to ensure that manufacturers of such devices can obtain robust information about the performance of their devices. The gravimetric method is one of the most common methods for the traceability of quantities and flow rates. It has the great advantage that it is a direct method, i.e., a measurement method in which the value of the measurand is determined directly without any calculation and traceability is straightforward. In contrast, it is much more complex to perform traceability of the alternative optical methods such as front tracking and micro-Particle Image Velocimetry (microPIV, uPIV) used at nanoflow. Compared to the gravimetric method, these methods can be used for even lower flow rates, but in turn can have much larger measurement uncertainties. Another outstanding advantage is that changes in flow rate can be seen immediately in real time based on the weight values and no post-processing of image data is necessary, as is the case with the two optical methods. This allows a full characterisation of the behaviour of drug delivery devices (infusion devices) and in-line sensors. Some National Metrology Institutes (NMI) have established infrastructures for testing the most commonly used infusion devices in hospitals, such as syringe pumps and Infusion Device Analyser (IDA), i.e., for flow rates down to about \(1\,\mathrm{mL}\,\mathrm{h}^{-1}\) (\(16\,667\,\mathrm{mL}\,\mathrm{min}^{-1}\)). Of these NMIs, at most, five are capable of measuring flow rates down to about \(100\,\mathrm{mL}\,\mathrm{min}^{-1}\). However, this flow range is not sufficient to investigate, for example, pain pumps (intrathecal pumps) and insulin pumps as these drug delivery devices administer very small volumes at ultra-low flow rates. For therapeutic purposes, pain pumps have programmable flow ranges down to \(2\,\mathrm{mL}\,\mathrm{h}^{-1}\) (\(33.333\,\mathrm{nL}\,\mathrm{min}^{-1}\)) and, for non-therapeutic purposes, the pumps can usually deliver even smaller flow rates down to \(0.25\,\mathrm{mL}\,\mathrm{h}^{-1}\) (\(4.167\,\mathrm{nL}\,\mathrm{min}^{-1}\)), which is about the same as the lowest flow rate for insulin pumps. To the best of our knowledge, there is no traceable test facility based on the dynamic gravimetric method available worldwide for flows down to about \(5\,\mathrm{nL}\,\mathrm{min}^{-1}\) as the measurement uncertainty at nanoflow increases substantially with decreasing flow rate. At these low flows, environmental uncertainties (variations in ambient temperature, air pressure and humidity), smallest impurities in the test liquid, air bubbles, uncertainties of the microbalance (linearity and drift) as reference and other measuring instruments, capillary effects, buoyancy effects, suction effects, stick/slip of the test liquid, jet forces on the microbalance and immersed tube, water absorption, but also possibly other effects, become very important. Evaporation becomes the most critical error component. Measurements with flow rates down to \(5\,\mathrm{nL}\,\mathrm{min}^{-1}\), with a measurement uncertainty of \(\mathrm{U}(k=2)\leq 5.0\%\), probably represent the range of feasibility using the dynamic gravimetric calibration method.