This is a series of notes dealing with several aspects of the problem of the interpretation of refraction data. A method of dealing with unreversed refraction lines is outlined. The case of a high velocity section with an overburden having a linear increase of velocity with depth is discussed. We show how the accuracy of the relative depth calculations depends upon the difference between the upper and lower velocities at the interface in question. A method of computing tables for the linear velocity depth case is given which is well adapted to machine calculation. Finally, reflections at the ground-air interface and the formation of shadows by such obstacles as high or low velocity layers are considered.