Sometime ago TELI created a one page GPS position solution in Mathcad.  It is a busy and interesting page.  It starts with satellite ephemeris and pseudorange data as inputs and calculates the position of the receiver antenna first in earth centered xyz coordinates and then translates these to the lat/lon position.   Below is a barely legible view of that page.  For a clear view,  download the .pdf file of it below.

Mathcad Position Solution - One Page Figure - Acrobat pdf format

Mathcad Position Solution - Description Document - Acrobat pdf format

If you do not have Adobe Acrobat Reader, it is available free download at the following link: