1. Using experimental setup, measure the hyperfine coupling constant a_1 for the isotope witch known I_1 and \mu_1

2. Again measure the hyperfine coupling constant but now a_2 for the isotope witch known I_2 but unknown \mu_2

3. Assume that J and B(0) is the same for both isotope I_1 and I_2, then by dividing constant we obtain:
a_2/a_1=\frac{\mu_2B}{I_2J}\times\frac{I_1J}{\mu_2B}=\frac{a_2I_2\mu_1}{a_1I_1}

Finaly we can derive the formula for \mu_2, that is \frac{a_2\mu_1I_2}{a_1I_1}, by substituting the known and experimentally determined values (\mu_1, I_1, I_2, a_1, a_2) ​​we get the value of \mu_2