What is a critical factor in obtaining an accurate compass reading?

Magnetic declination is a critical factor in obtaining an accurate compass reading because it refers to the angle between magnetic north (the direction the compass points) and true north (the geographical north pole). This angle varies depending on where you are located on the Earth’s surface and can change over time due to fluctuations in the Earth's magnetic field.

When taking compass readings, especially in navigation and surveying, it is essential to apply the correct magnetic declination adjustment. Failure to account for this declination can lead to significant errors in direction, which can affect the accuracy of surveys or navigation. Therefore, understanding and applying the appropriate magnetic declination is vital for ensuring the reliability of compass readings.

While other factors like weather conditions, the age of the compass, and the duration of measurement may influence the compass performance or the accuracy of the method used, none is as essential for correcting the compass reading as magnetic declination, which directly impacts the alignment between the compass reading and true geographic references.