[经] stability of the measuring unit

héng liáng dān wèi de wěn dìng xìng ㄏㄥˊ ㄌㄧㄤˊ ㄉㄢ ㄨㄟˋ ㄉㄜ˙ ㄨㄣˇ ㄉㄧㄥˋ ㄒㄧㄥˋ