...or the two stolen pixels.
With the vector-skin it's hard to setup bigger fonts for text body . Even with 18px one get's only 14px (rounded). And my convinient setting was 17px resulting in 16px font size on MonoBook. The Table below lists the scaling result depending on settings.
127%*x-small = MonoBook
0.8*medium = Vector
medium° | x-small | 127%*x-small | 0.8*medium
12px | 9px | 11.43px | 9.6px
13px | 10px | 12.7px | 10.4px
14px | 10px | 12.7px | 11.2px
15px | 10px | 12.7px | 12px
16px | 10px | 12.7px | 12.8px (default setting)
17px | 12.75px | 16.1925px | 13.6px (=14px)
18px | 13.5px | 17.145px | 14.4px (=14px!)
°medium = browser setting
Since target size is 13px it would lead to more comfortable configuration options when setting scaling factor to 13/16 = 0,8125.
medium | (0.8125*medium)
12px | 9.75px
13px | 10.5625px
14px | 11.375px
15px | 12.1875px
16px | 13px
17px | 13.8125px (=14px)
18px | 14.625px (=15px)
By the way google search uses small for scaling textbody, which gives best results in upscaling fonts, also it's less predictable what exactliy is happening.
Should affect opera, chrome and safari as well, but on IE there is no way in setting font size directly by numbers.