Harmonic Theory shows that the Earth’s magnetic field is unbalanced, with **1850 lines per square cm** in one direction and **1257 lines per square cm** in the other direction. To see how they fit into the overall harmonic system, these measurements must be first converted to the grid system. This was not specifically outlined in Bruce Cathie’s books, so it will be shown here.

Here is the conversion of the two fields:

**Geodetic Conversions for Magnetic Field of the Earth**

In the first section, the object is to calculate a conversion factor to go from centimeters per standard inch to centimeters per geodetic inch.

The next section shows the theoretical values of each field. Due to the curvature of the Earth, the the 1850 value works out to be a little more than 1853, and the 1257 value works out to be a little more than 1259.

The third section shows the conversion of the 1853 lines of force to square geodetic inches.

The fourth section shows the conversion of the 1259 lines of force to square geodetic inches.

Hopefully, this makes things clearer for readers of Bruce Cathie’s books.