SailNet Community - View Single Post - Magnetic Variance
View Single Post
Old 01-29-2014
Dean101's Avatar
Dean101 Dean101 is offline
Life is a wild ride!
Join Date: Apr 2011
Location: Kentucky
Posts: 409
Thanks: 6
Thanked 3 Times in 3 Posts
Rep Power: 5
Dean101 is on a distinguished road
Question Magnetic Variance

I've been reading up on charts and how to plot bearings. The books I have all seem to describe converting magnetic bearings to true bearings in the same way and they have me confused.

I understand that the variance given in the compass rose has a stated variance, when it was measured, and the amount and direction of change per year. I understand how to find the current year variation from this information. What's confusing me is the statement "To convert a magnetic compass reading to true to plot on a chart *subtract a westerly variation *Add an easterly variation."

Assuming that my variation after figuring for current year is 5* W. and forget deviation for a moment, let's say I take a compass bearing of 270*. Would my conversion be 270 - 5 = 265*T? If the variance was 5* E then the conversion would be 270 + 5 = 275*T?

I'm not sure why I'm having so much trouble picturing this in my head.
Reply With Quote Share with Facebook