[填空题]
The first length standard, fh1wwzt /z :3 awr7a7zadopted in the 18u,*ar ktl9h,g$^{th}$ 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} $
