Uncertainty in the position of an electrons (mass = $9.1\times {10}^{-31}kg$) moving with a velocity $300m{s}^{-1}$,accurate up to 0.001% will be

$p=m\upsilon =(9.1\times {10}^{-31}kg)\left(300m{s}^{-1}\right)=27.3\times {10}^{-29}kgm{s}^{-1}$

            $\Delta p=\left(0.001\%\right)p=\left({10}^{-5}\right)(27.3\times {10}^{-29}kgm{s}^{-1})=27.3\times {10}^{-34}kgm{s}^{-1}$

            $\Delta x=\frac{1}{\Delta p}\left(\frac{h}{4\pi }\right)=\frac{1}{(27.3\times {10}^{-34}kgm{s}^{-1})}\left(\frac{6.626\times {10}^{-34}Js}{4\times 3.14}\right)=0.0192m$