研究人员经常测量婴幼儿的体长——从每天到一周两次不等——并且参照睡眠记录。
The researchers measured the infants' length often - anywhere from daily to twice a week - and cross-referenced their growth with parents' sleep records.
2003年发射的冰云和地面高度卫星对北极圈区域进行的测量给这项研究提供了参照。
The study looked at measurements taken of the Arctic region by the Icesat satellite, launched in 2003.
到目前为止，类星体是测量地球自转最好的参照系。
Quasars are so far away that they constitute the best frame of reference for measuring Earth's rotation rate.
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