DOF calculation

Correct!  Back when lenses had depth of field scales on them, different brands might show different depth of field ranges for the same aperture, focal length, and focus distance.  For example, my 50mm F/1.9 Schneider-Kreuznach Xenon F/1.9 is a bit less generous with the expected depth of field than my 50mm f/1.7 Zeiss Planar.  The Cambridge in Colour tutorial notes that lens manufacturers did not assume perfect vision when they developed their depth of field scales, saying, "People with 20/20 vision can perceive details which are roughly 1/3 the size of those used by lens manufacturers  . . . to set the standard for lens markings."

In the end, we each need to experiment to find the settings that work for us, that we're happy with.  I've typically found that rather loose standards for depth of field still render images that I find acceptably sharp.  Others may well have more critical needs.