Counters: the enclosed or partially enclosed circular or curved negative space (white space) of some letters such as d, o, and s is the counter.
Aperture: The partially enclosed, somewhat rounded negative space in some characters such as ‘n’, ‘C’, ‘S’, the lower part of ‘e’, or the upper part of a double-storey ‘a’. Specifically the opening to the counter space.
The counters in letters have a crucial role in the performance of
the text viewed at a distance.
The typefaces with small counters
and closed apertures perform low in legibility and small sizes
are apparently unreadable.
The phenomenon of irradiation and
chromatic aberration around the outlines of the letters fills up the
counters and small apertures make the letters like c, e appear
as o (see image).
Typefaces like Helvetica, Univers which are
heavily used in most screen and print jobs are unsuitable for distance
Large x-height has a direct impact on counter size but wider letter shapes are better as they reduce the perspective distortion. Since most of the text in XR is placed in the vertical plane in front of the user.
If the text is placed in the horizontal plane then the impact of x-height is more.