Headlamp aim is a complex vehicle feature which is important for customer safety, and faults in the assembly adjustment process represent an important aspect of automotive faults. This paper examines the issue of headlamp aim through defining the fundamentals of headlamp aim, the different methods of aim setting, analysing two different aim measurement systems, and outlining the factors which cause variation in this vehicle characteristic. The results of conducted testing isolated the significant variables which influenced vertical headlamp aim. These factors were then utilised in the development of appropriate plant and customer specifications. For the vehicle types examined in this research, fuel tank quantity was found to be the most significant variable in terms of influencing headlamp aim from the plant to the customer. Through an understanding of variability in vertical headlamp aim (both setting and post-production variation) vehicle manufacturers can more accurately assess the different types of headlamp machinery in terms of their ability to meet required levels of customer satisfaction. The approach presented is not unique to headlamp aim and the principles are relevant to other vehicle features which must conform to a certain specification.