Definition of rotated astigmatism

1. in the measurement of photolithographic instruments, at each image site, the Z-axis difference for the line focus of two evaluative line sets, oriented at right angles to each other and at some specified angle to the coordinate system, where the specified angle is selected so that the Z-axis focus difference is a maximum at the given image site. The specified angle may vary from image site to image site. [SEMI P25-94]