The plane of the dip circle is set in the geographical meridian and the apparent dip is ${\mathrm{\theta }}_1$. It is then set in a vertical plane perpendicular to the geographical meridian, the apparent dip becomes ${\mathrm{\theta }}_2$. The angle of declination $\mathrm{\alpha }$ at that place is given by

• A

  $\tan \mathrm{\alpha }=\sqrt{\tan {\mathrm{\theta }}_1 {\mathrm{tan\theta }}_2}$

• B

  $\mathrm{\alpha }=\sqrt{{\tan }^2 {\mathrm{\theta }}_1 {\tan }^2 {\mathrm{\theta }}_2}$

• C

  $\tan \mathrm{\alpha }=\frac{\tan {\mathrm{\theta }}_1}{{\mathrm{tan\theta }}_2}$

• D

  $\tan \mathrm{\alpha }=\frac{\tan {\mathrm{\theta }}_2}{{\mathrm{tan\theta }}_1}$