This paper presents a tutorial on the methods that can be used to analyse and predict the errors for near-field antenna measurements. The paper makes use of an 18-point uncertainty budget [1] for antenna gain measurements in a planar range and adapts it for other types of measurement, such as gain measurements in a spherical near-field range. It discusses the form the errors can take and how to identify and measure them. It also looks at the techniques available for combing the effects of the identified errors into an uncertainty budget.