Magnetic Bearing A magnetic bearing is a bearing where the Magnetic North line is taken as 0  A compass points towards the magnetic north pole which is not True North Magnetic North True North ? ? On South African maps Magnetic North will always be to the left i.e. West of True North

True North is the point around which the earth rotates True/Geographic North Magnetic North

Magnetic Declination The measurement in degrees between True North and Magnetic North Magnetic North TN True North TN True North The Magnetic North is not a fixed position. ? ?

Magnetic Declination The measurement in degrees between True North and Magnetic North Magnetic North TN True North TN True North The Metrication of degrees and minutes There are 60 minutes in 1 degree Metrication is dividing the 60 minutes into 10. So one decimal point = 6 minutes 0,  5 = 30 minutes Just multiply metricated degrees by 6 to convert back Metricated degrees are represented 20,  3 west of True North (Twenty degrees and 18’ [minutes] west of True North) ? ?

Magnetic Declination The measurement in degrees between True North and Magnetic North Pietermaritzburg Map Example 1.So the angle between True North and Magnetic North was 20  18’ (20,  3) in Magnetic North as calculated in this area was changing at an average of 2’ per year to the east. ( ) Magnetic North TN True North TN True North 20,  3 Mean magnetic declination 20,  3 west of True North (1981.0). Mean annual change 2’ eastwards ( ) Mean magnetic declination 20,  3 west of True North (1981.0). Mean annual change 2’ eastwards ( ) When working with a map or compass we have to calculate PRESENT Magnetic Declination

Magnetic Declination The measurement in degrees between True North and Magnetic North Pietermaritzburg Map Example 1.So the angle between True North and Magnetic North was 20  18’ (20,  3) in Magnetic North as calculated in this area was changing at an average of 2’ per year to the east. ( ) When working with a map or compass we have to calculate PRESENT Magnetic Declination Pietermaritzburg Map Example 1.Present year = Map date of magnetic declination = Difference in years = 30 years 4.Annual change = 2’ east 5.Annual change multiplied by difference in years 2’ X 30 = 60’ east 6.Direction of change is East therefore SUBTRACT 7.Subtract total change = 20  18’ minus 30’ 8.Magnetic declination for 2011 = 19  48’ west of true north Pietermaritzburg Map Example 1.Present year = Map date of magnetic declination = Difference in years = 30 years 4.Annual change = 2’ east 5.Annual change multiplied by difference in years 2’ X 30 = 60’ east 6.Direction of change is East therefore SUBTRACT 7.Subtract total change = 20  18’ minus 30’ 8.Magnetic declination for 2011 = 19  48’ west of true north If the average change is to the east-> SUBTRACT total change If the average change is to the west-> ADD total change

Magnetic Declination Pietermaritzburg Map Example 1.Present year = Map date of magnetic declination = Difference in years = 30 years 4.Annual change = 2’ east 5.Annual change multiplied by difference in years 2’ X 30 = 60’ east 6.Direction of change is East therefore SUBTRACT 7.Subtract total change = 20  18’ minus 60’ 8.Magnetic declination for 2011 = 19  18’ west of true north Pietermaritzburg Map Example 1.Present year = Map date of magnetic declination = Difference in years = 30 years 4.Annual change = 2’ east 5.Annual change multiplied by difference in years 2’ X 30 = 60’ east 6.Direction of change is East therefore SUBTRACT 7.Subtract total change = 20  18’ minus 60’ 8.Magnetic declination for 2011 = 19  18’ west of true north If the average change is to the east-> SUBTRACT total change If the average change is to the west-> ADD total change The Steps used in the calculation 1.When was the magnetic declination of the map calculated? 2.Work out the difference in years between present time and your answer to 1. above 3.What was the average change per year? 4.Calculate the total change –the average change per year X difference in years 5.If …. 6.You now have the map declination for the present time

Exercise 1.Using the Alberton Map calculate the Magnetic Declination for this year Magnetic North TN True North TN True North 17 ,0 Mean magnetic declination 17,  0 west of True North (1977.0). Mean annual change 4’ eastwards ( ) Mean magnetic declination 17,  0 west of True North (1977.0). Mean annual change 4’ eastwards ( )

Exercise 2. Using the Plettenberg Bay Map calculate the Magnetic Declination for this year Magnetic North TN True North TN True North 23 ,6 Mean magnetic declination 23 ,6 west of True North (1977.0). Mean annual change 2’ eastwards ( ) Mean magnetic declination 23 ,6 west of True North (1977.0). Mean annual change 2’ eastwards ( )

Exercise 1.Using the Alberton Map calculate the Magnetic Declination for this year Magnetic North TN True North TN True North 17 ,0 Mean magnetic declination 17,  0 west of True North (1977.0). Mean annual change 4’ eastwards ( ) Mean magnetic declination 17,  0 west of True North (1977.0). Mean annual change 4’ eastwards ( ) Alberton Map Example 1.Present year = Map date of magnetic declination = Difference in years = 34 years 4.Annual change = 4’ east 5.Annual change multiplied by difference in years 4’ X 34 = 136’ east (2  16’) 6.Direction of change is East therefore SUBTRACT 7.Subtract total change = 17  0’ minus 2  16’) 8.Magnetic declination for 2011 = 14  44’ west of true north Alberton Map Example 1.Present year = Map date of magnetic declination = Difference in years = 34 years 4.Annual change = 4’ east 5.Annual change multiplied by difference in years 4’ X 34 = 136’ east (2  16’) 6.Direction of change is East therefore SUBTRACT 7.Subtract total change = 17  0’ minus 2  16’) 8.Magnetic declination for 2011 = 14  44’ west of true north

Exercise 2. Using the Plettenberg Bay Map calculate the Magnetic Declination for this year Magnetic North TN True North TN True North 23 ,6 Mean magnetic declination 23 ,6 west of True North (1977.0). Mean annual change 2’ eastwards ( ) Mean magnetic declination 23 ,6 west of True North (1977.0). Mean annual change 2’ eastwards ( ) Alberton Map Example 1.Present year = Map date of magnetic declination = Difference in years = 34 years 4.Annual change = 2’ east 5.Annual change multiplied by difference in years 2’ X 34 = 68’ east 6.Direction of change is East therefore SUBTRACT 7.Subtract total change = 23  6’ minus 68’ 8.Magnetic declination for 2011 = 21  58’ west of true north Alberton Map Example 1.Present year = Map date of magnetic declination = Difference in years = 34 years 4.Annual change = 2’ east 5.Annual change multiplied by difference in years 2’ X 34 = 68’ east 6.Direction of change is East therefore SUBTRACT 7.Subtract total change = 23  6’ minus 68’ 8.Magnetic declination for 2011 = 21  58’ west of true north