In 1960 Roland G. Henderson, of the U.S. Geological Survey, published a comprehensive system for computation of first and second derivatives of potential fields
and the continuation of fields to levels above or below the plane of observation. In our study a Fortran IV program (HNDRSN2), based on Henderson's algorithm,
uses map data digitized at an equally spaced grid interval. Output from program HNDRSN2 includes maps of the field continued upward or downward from one
to five grid units and first and second derivative maps on the surface and on selected downward continued levels. Test cases demonstrate the reliability of the
program in standard analyses of gravity and magnetic fields
