\left\Vert \overrightarrow{B_{1}}\right\Vert = K \left\Vert \frac{\overrightarrow{p}}{p^{3}} - \frac{\overrightarrow{r}} {r^{3}} \right\Vert = \frac{K}{r^2} \left\Vert \frac{r^2}{p^2} \frac{\overrightarrow{p}}{p} - \frac{\overrightarrow{r}}{r} \right\Vert = \frac{K}{r^2} \sqrt{\frac{r^4}{p^4} - 2 \frac{r^3}{p^3} \frac{\overrightarrow{p}.\overrightarrow{r}}{r^2} +1}