Physical model testing forms a critical part of the development process for offshore renewable energy (ORE) technologies. Devices and structures generally follow a Technology Readiness Level (TRL) development pathway which has nine steps ranging from the initial idea (TRL1) to commercialisation (TRL9). In ORE, technologies are tested extensively in laboratory environments up to TRL4 after which a decision is made as to whether a particular technology has sufficient potential to justify moving to open sea environments where the costs can be much higher. Therefore, physical model testing plays a critical role in the development process and in recent years increased emphasis has been placed on improving quality procedures and implementing best practice methodologies. The International Towing Tank Conference (ITTC) and the International Electrotechnical Commission (IEC) have been developing testing standards whilst European Union funded projects such as Equimar, MaRINET and MaRINET2 have been working with testing infrastructures in developing a more uniform approach to testing. However, a standardised approach to the assessment of uncertainty in physical testing has yet to emerge. This paper focuses on and estimates the variation associated with wave elevation measurements using conductive wave probes in a hydraulics laboratory, a key input in all physical testing analysis.