Relative variation of the axial frequency versus the modified-cyclotron radius of an ion with mass-to-charge ratio of 187. The -axis is plotted up to , which is the limit to maintain the coupling between the ion of interest and the sensor ion [27]. Using (2.9) and (2.10), the pairs 187Re+-40Ca+ and 187Os+-40Ca+ are coupled if their oscillation frequencies (we consider kHz) are equal within 29 mHz [27]. The ions are moving in a 7 T magnetic field, so that (187Re+) = 565282.43 Hz.
