GL-3 National Romanization-- Keep, Change, Add! 國語羅馬字：留、改、加！

Variations of the base form (initial, medial and final) of National Romanization are used to spell the four tones of mandarin Chinese. Words spelled in National Romanization (Gwoyeu Luomaatzyh) have distinctive shapes which are easy to recognize. This is especially helpful for foreigners struggling to learn the four tones of Mandarin Chinese. 國語羅馬字靠基本形式（聲母、介音、韻母）的不同拼法來表示漢語的四聲。『留、改、加』這三個原則使『國羅』拼出來的字，個個有其獨特風貌、易於辨認。對於外國人學習國語的聲調非常有幫助。

1 Keep留: Keep the unchanged base form; Use it to spell most first tone words and all second tone words starting with m-, n-, l- or r. 保留基本形式，用來拼寫一般陰平（一聲）字及ㄇㄋㄌㄖ開頭的陽平（二聲）字

2 Change改: Change the base form. Use a different spelling of the medial vowel or a final glide to show the second and third tones, and certain fourth tone words. 改變基本形式：陽平、上聲以及小部分去聲字（二、三、四聲字），盡量改拼介音或韻尾

3 Add加: If there is no medial vowel, final glide or consonant that can be respelled, add a letter. 沒有介音、韻尾可供改拼，根據基本形式加字母