Now that the thread has started [thanks KWIL] …
The ‘Home Made Precision Optics’ [Optical Centre Punch] article contains a couple of oddities, which I must have overlooked the first time:
On p30, col.3 : “Acrylic is not quite so easy to machine as Perspex”
On p31, bottom : “A good view showing the inked cross-hairs”
Both of these statements need explanation/justification/context
MichaelG.