# How many "microns" in a length of 670*nm?

$670 \cdot n m$ $=$ $670 \times {10}^{-} 9 \cdot m$
And $670 \times {10}^{-} 9 \cdot m = 6.70 \times {10}^{2} \times {10}^{-} 9 \cdot m = 6.70 \times {10}^{-} 7 \cdot m$
$=$ $0.670 \times {10}^{-} 6 \cdot m$ $=$ $0.670$ $\mu$, where $\mu \equiv 1 \times {10}^{-} 6 \cdot m$.