Vertical Angle Jump at Transit The above plot, graciously provided by Bruce Macintosh and Christian Marois, shows the shift in the pupil plane that occured during transit while tracking an object in vertical angle mode. The curve of the object's location in the images (somewhat quantized) is due to expected (vertical angle mode) field rotation (shown as stars). The jump between images 120 and 140 is due to the tracking shift and shows that this tracking mode, which does hold a constant vertical angle, also results in an image location jump in the frame of the pupil. The differences between PARANG and PARANTEL, as read from the image headers, are over-plotted on this same plot (shown as diamonds). This latter plot provides a second visualization of the difference between fixed-pupil and fixed-vertical-angle.