The uncertainty in the location of circulating electron is equal to its de Broglie wavelength. The minimum percent error in its measurement of velocity under this circumstances will be approximately

Let the electron be moving with momentum, p, its wavelength will be equal to h/p.λ=hp=∆xFrom Heisenberg's uncertainty principle,Δx × Δp  =  h4πΔpp=  14πMinimum percent error in measuring its velocity would be100 × Δvv  = Δpp× 100  =1004π=1004×3.14                   =7.96  ≈  8