Summary—A simple device for testing urine flowmeters is described. It is made from readily available components and is portable, easy to use, and requires no special care in setting up. The flow rate is accurate to within 0.5 ml/s. Nursing staff are now able to do regular calibration checks on the urine flowmeters and some flowmeter deficiencies have been exposed. Using the tester, examples of artefactual peak flow rates have been recorde