sentence: non-si units of length include : fermi ( fm ) ( = 1 femtometre in si units ) ångström ( å ) ( = 100 picometre in si units ) micron ( = 1 micrometre in si units ) norwegian/swedish mil / myriametre ( = 10,000 metres ) x unit ( = 0.1 picometre ) imperial/us the basic unit of length in the imperial and u.s. customary systems is the yard , defined as exactly 0.9144 m by international treaty in 1959 .