In a vertical plane at `30^(@)` from the magnetic meridian, the horizontal component is,
While vertical component is still. Thereofre, apparent dip will be given by `tan theta'=(V)/(H)=(V)/(H cos30^(@))`
`but " " (V)/(H)=tan theta' " " (where theta= "true angle of dip")`
`therefore " " tan theta'=(tan theta)/(cos 30^(@))`
`therefore " " theta=tan^(-1)[tan theta'cos30^(@)] `
`therefore " " a=tan^(-1)[(tan45^(@))(cos30^(@))]approx41^(@) `