VicRoads allows user to install engine gauges to their car providing the following is followed.
Gauges may be forward of the windscreen in a position visible to the driver provided they meet the following requirements which are effectively the same as the

bonnet scoop and protrusion requirements


πŸš™ The gauges or any attaching brackets or covers must be of a smooth construction with the edges suitability radiused so that they are not likely to increase the risk of injury to a person
πŸš™ The surface or any part of the gauge or cover visible to the driver must not be more reflective than the general bodywork of the vehicle


πŸš™ If the gauges have instrument lighting, then the intensity of the light must not be greater than that of the interior panel


πŸš™ The gauges or cover must not prevent the river from having a clear uninterrupted view through the full width of the windscreen of all parts of the road surface 11 meters forward of the steering wheel viewed from any driving position permitted by the range of the adjustment of the driver’s seat


πŸš™ If the gauges or mounting brackets have sharp edges or are constructed in such a way that the likelihood of an injury to a person is increased, then they must be covered by a fairing which presents a smooth surface when viewed from the front and side of the vehicle

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Link to all VSI (Vehicle Safety Information) Sheets