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The metre (international spelling) or meter (American spelling) (from the Greek noun μέτρον, "measure") is the base unit of length in the International System of Units (SI). The SI unit symbol is m. The metre is defined as the length of the path travelled by light in a vacuum in 1/299 792 458 seconds.
微米(SI符號:μm)或千分尺是長度等於1米×10-6(SI標準前綴“微 - ”= 10-6)的SI導出單位; 即百萬分之一米(或千分之一毫米,0.001毫米或約0.000039英寸)。