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**Example:** A surveyor measures the total magnetic field strength at a site to be **B = 55 µT** and the inclination angle to be **I = 45°**. Find the horizontal component **B_h** of the Earth's magnetic field at that location. **Steps:** 1. Write the formula for the horizontal component: \(B_h = B \times \cos I\). 2. Convert the inclination angle to radians if using a calculator that requires radians, or directly use the cosine function in degree mode. 3. Calculate \(\cos 45°\). \(\cos 45° = \frac{\sqrt{2}}{2} \approx 0.7071\). 4. Multiply the total field by the cosine value: \(B_h = 55\,\mu T \times 0.7071 \approx 38.9\,\mu T\). 5. **Result:** The horizontal component of the magnetic field is approximately **38.9 µT**. This horizontal component is what a compass would primarily respond to at that location.