栢史 (*CAsi)
In Old Korean orthography, native terms with clear Chinese equivalents are usually written with an initial Chinese character (logogram) glossing the meaning of the word, followed by one or more Chinese characters (phonograms) that transcribe the final syllable or coda consonant of the term. In the case of 栢史, the first character shows that this is the native Old Korean word for either Korean pine (Pinus koraiensis or Chinese arborvitae (Platycladus orientalis), and the subsequent character shows that the coda consonant of this word is *si.
Middle Korean for "Korean pine" is 잣〯 (Yale: cǎs), with a rising tone marked by the two dots on the left and the accent on the romanization. As Middle Korean rising tone comes from an Old Korean bisyllabic form, the Old Korean word 栢史 is conventionally reconstructed as *CAsi, where the final vowel was dropped but left its trace in the tonal pattern to produce the Middle Korean form.
According to scholarly convention, the elements of the reconstruction which are not directly represented by phonograms are given in capital letters. This allows readers to identify what part of the reconstruction is attested and what part is applied retroactively from the Middle Korean reflex.
Some academic readings postulate *CAs, simply casting back the Middle Korean reflex, but this is problematic both because the consonantal phonogram 叱 (*-s) would then be expected, and because it fails to take into account the Middle Korean tone.