An instrument is described that permits the measurement of scattered light on windshields in cars in full daylight. It presents the intensities of the scattered light in the form of a diagram and calculates two indices, which can be associated with the most prominent types of wear, i.e., impact of small stones and wiper damage.

The instrument is easy to operate and permits inspection of a large number of windshields in a short time. Measurements on 300 vehicles indicate a linear increase in wear due to impact of small stones with mileage and a more-than-linear increase of wiper damage. Vehicles of identical mileage can have very different values depending on the type of use.

It is also examined how the different amounts of wear as characterized by the measured indices affect the ability of test persons to see and recognize objects on the road.