Why resulting deviation from HSI remain same in all latitude?
Ships HSI (F&A, athwartship) induced by only H.
We know, If magnetic latitude change – DF(H) change.
But, deviating force due to DF(H) also change.
Therefore, we can tell, if DF(H) get bigger deviating force get bigger.
If DF(H) get smaller deviating force get smaller.
Again, we also know, If magnetic latitude increase – DF(H) get smaller (deviating force get bigger)
So, resulting deviation from HSI remain same in all latitude.