I have not been following List postings very closely for some time, but a recent attempt to catch up made me realize that much attention has been given to shadow sharpeners re John's Kitt Peak project.
This leads me to ask: What efforts have been made to assess the straightness and 'truth' of those edges of the rhomboidal prismoid gnomon structure, which are intended to serve as styles? A quick survey of photos accompanying the proposal is not reassuring on this score. In those areas of the images where the edge profiles are distinguishable through contrast against the sky, or by a shadow boundary, their erose nature is quite evident. Estimating the size of these defects from computer screen views of scanned photos is an uncertain matter, but it certainly raises questions. As the 1/2 degree solar disk swings back and forth seasonally through its arc of nearly 47 degrees, it would serve little purpose to determine its precise position relative to an inaccurate and varying traversed edge. It is often all too easy to be 'precisely wrong'. Sciagraphically, Bill Maddux -
