tones. Such notations are especially common when comparing dialects with wildly different phonetic realizations of what are historically the same set of tones. In Chinese, for example, the "four tones" may be assigned numbers, such as ① to ④ or – after the historical tone split that affected all Chinese languages to at least some extent – ① to ⑧ (with odd numbers for the yin tones and even numbers for the yang). In traditional Chinese notation, the equivalent diacritics are attached to the Chinese character, marking the same distinctions, plus underlined for the yang tones where a split has occurred. If further splits occurred in some language or dialect, the results may be numbered '4a' and '4b' or something similar. Among the Kradai languages, tones are typically assigned the letters A through D or, after a historical tone split similar to what occurred in Chinese, A1 to D1 and A2 to D2. (See Proto-Tai language.) With such a system, it can be seen which words in two languages have the same historical tone (say tone ③) even though they no longer sound anything alike. Also phonemic are upstep and downstep, which are indicated by the IPA diacritics and , respectively, or by the typographic substitutes and , respectively. Upstep and downstep affect the tones within a language as it is being spoken, typically due to grammatical inflection or when certain tones are brought together. (For example, a high tone may be stepped down when it occurs after a low tone, compared to the pitch it would have after a mid tone or another high tone.) Phonetic notation records the actual relative pitch of the tones. Since tones tend to vary over time periods as short as centuries, this means that the historical connections among the tones of two language varieties will generally be lost by such notation, even if they are dialects of the same language. The easiest notation from a typographical perspective – but one that is internationally ambiguous – is a numbering system, with the pitch levels assigned digits and each tone transcribed as a digit (or as a sequence of digits if a contour tone). Such systems tend to be idiosyncratic (high tone may be assigned the digit 1, 3, or 5, for example) and have therefore not been adopted for the International Phonetic Alphabet. For instance, high tone is conventionally written with a 1 and