2. Explain why the calculation in Step 14 in section 2.2 is correct. (Hint: what if the Earth's magnetic field was purely vertical at your location? What if it was 1 degree away from vertical?) Step 14 In the Excel workbook, calculate the angle the Earth's magnetic field lines make with the Earth's surface. That angle is 90 degrees minus the average angle from the horizontal measured for your screen in Step 7. (Here we are ignoring the direction of the magnetic field.)