low tone with a 4 or 5 when transcribing the Kru languages of Liberia, but with 1 for low and 5 for high for the Omotic languages of Ethiopia. The tone in a Kru language is thus the same pitch contour as one written in an Omotic language. Pitch value 1 may be distinguished from tone number 1 by doubling it or making it superscript or both. For simple tone systems, a series of diacritics such as for high tone and for low tone may be practical. This has been adopted by the IPA, but is not easy to adapt to complex contour tone systems (see under Chinese below for one workaround). The five IPA diacritics for level tones are , with doubled high and low diacritics for extra high and extra low (or 'top' and 'bottom'). The diacritics combine to form contour tones, of which have Unicode font support (support for additional combinations is sparse). Sometimes, a non-IPA vertical diacritic is seen for a second, higher mid tone, , so a language with four or six level tones may be transcribed or . For the Chinantecan languages of Mexico, the diacritics have been used, but they are a local convention not accepted by the IPA. A retired IPA system, sometimes still encountered, traces the shape of the tone (the pitch trace) before the syllable, where a stress mark would go (e.g., ). For a more concrete example, take the Hanyu Pinyin syllable [sa] used in Standard Chinese, after applying the diacritics it becomes easier to identify more specific rising and falling tones: (high peaking tone), (low level tone), etc. It was used in combination with stress marks to indicate intonation as well, as in English (now transcribed ). The most flexible system, based on the previous spacing diacritics but with the addition of a stem (like the staff of musical notation), is that of the IPA-adopted Chao tone letters, which are iconic schematics of the pitch trace of the tone in question. Because musical staff notation is international, there is no international ambiguity with the Chao/IPA tone letters: a line at the top of the staff is high tone, a line at the bottom is low tone, and the shape of the line is a schematic of the contour of the tone (as visible in a pitch trace). They are most commonly used for complex contour systems, such as