[填空题]
The first length stanqwd xxny598 :tf 2 ypa(3sf;6eliecx: to d);x8xtu:t5y1csv dard, adopted in the 18$^{th}$ century, was a platinum bar with two very fine marks separated by what was defined to be exactly 1 m. If this standard bar was to be accurate to within $\pm1.0 \mu m$ how carefully would the trustees have needed to control the temperature? The coefficient of linear expansion for platinum is $ 9\times10^{ -6}C/^{-1}$. $\pm$ = C$^{\circ} $
