Originally Posted by
militarymoron
the utility of a 'absolute/true' co-witness, IMHO, is as a sanity check to see if anything has shifted, or checking that you optic is still zeroed when you remove and replace it. the dot doesn't have to be co-zero'd with the irons to do that - you can zero the dot independantly, then check to see where it is in relation to the front sight when looking through the irons (windage should be centered, but you can be 'one dot width' above the FSP, etc).
normally, you'd never look through the irons when using the dot. i agree - it defeats the purpose. however, there have been instances where i HAVE utilized the rear aperture with the dot to sharpen it up. the sharpness of the dot depends mostly on your vision. my eyesight isn't that good, and using the small rear aperture when sighting in the dot, or for longer ranges on small targets acts like almost like a pinhole camera and sharpens up a dot that might appear a bit blur or fuzzy. for those with less than perfect vision, look at your dot, then flip up the rear sight with the small apreture and look through it again. chances are you'll see a sharper, more distinct dot.
i think the point of brett's original post was to try to get some agreement/standardization on the terms used. here are my suggestions for defining the terms:
Co-witness - the ability to view the irons sights through the tube. This applies to any height of the optic relative to the irons, as long as they can be seen. the dot can be adjusted to the irons or zero'd independantly.
Co-zero'd - i suggest discarding the terms 'absolute' or 'true' co-witness as they're confusing. this is when the dot is adjusted so it sits on top of the FSP when looking through the irons. the zero will only be valid for the distance they're both zero'd at.