While you are on the site, in your browser find and click "Add to Home Screen" A CGN beaver app icon will then be created to your phone that is directly link to the site.
Note: This feature may not be available in some browsers.
Most (like mine) use a screw-clamp arrangement, although some are just drifted in. If yours is the screw type, you will see a little "blade" in the front (muzzle end) of the sight base. This is a reverse-head screw, ie rather than a slot, it has a ridge or blade (Perverse but true!) There are special tools available for this, of course, but you can make one by taking an old screwdriver (or a spare blade for a multi-bit screwdriver), cutting the blade off (which will leave you with the shank) and using a Dremel with a cut-off wheel to cut a slot in it.
Hope this helps. If it's not clear, e-mail me (josquin@ shaw.ca) and I'll send some photos.