The ‘mathematical’ alignment is usually just considered "centered however the alignment button works in the software you're using" in design discussion. For mos

The ‘mathematical’ alignment is usually just considered "centered however the alignment button works in the software you're using" in design discussion. For most software that'd be bounding box based - the center of the rectangle the software draws around it. Optically is more center of mass, but ideal more 'center of visual weight'. Larger things are 'heavier', darker/more contrasty things are 'heavier'. Rounded things should extend over an alignment line a bit, flat shapes butt up against it (e.g. in the letters lO the O extends over the baseline slightly compared to the l, to visually connect with the baseline more). In general the way it works is you align with whatever software says and you look at it and say does it actually look aligned or need minor adjustment? Because the point is to look aligned rather than to be mathematically correctly aligned. Like our letters above, they look more visually on the same baseline when they're not, then when all the rounded base letters sit most 'correctly' on the line.