I measured the x-height, line spacing, and line length in 114 scientific journals, 110 novels, and 106 A5-size brochures (210 x 148.5 mm; 8.25[inches] x 5.75[inches]).
I took all measures - x-height, line spacing, and line length - in millimeters.
First, I will present the results of the x-height and line spacing measurements.
They measured the x-height in 100 American newspapers.
A second indication that typographic guidelines and practical documents differ is that the line spacing for type with the same x-height varies considerably.
Unfortunately, it is not possible to relate the actual measures of x-height and line spacing of text to the original point sizes in which a text was specified.
I took the most frequently appearing x-height in my study, 1.60 mm (0.06[inches]), as an example.
Table 1 shows that type with an x-height of 1.60 mm (0.06[inches]) and a line spacing of 4.25 mm (0.167[inches]) could have a body height between 7.1 points (Didot) and 11.4 points (pica).
It might be the case that the range of 1.30 mm to 1.90 mm for the x-height is similar to the range of 8-14 points body height.
Figure 7 shows a scatter plot of the relationship between x-height and line length in 110 novels.
The variation in line length for type with the same x-height is large.