In a device for determining the isotopic composition, potassium ions 39K+ and 41K+ are first accelerated in an electric field, and then fall into a uniform magnetic field of induction B, perpendicular to the direction of their movement. During the experiment, due to imperfection of the equipment, the accelerating voltage changes by ±∆V near its average value. With what relative error ∆V/V is it necessary to keep the value of the accelerating voltage constant so that the traces of potassium isotope beams on the photographic plate do not overlap?