A Mercator (rhumb-line) calculator for WGS84 is here. A beginning on a (mathematical!) primer on navigation on an ellipsoidal earth is here. I'm planning on getting this finished sometime...
A discussion of compass errors, with formulae is here.
I've written software that computes magnetic variation anywhere on (or above) the earth's surface, using either the WMM or IGRF reference models. There are Mac , DOS , linux , and Java executables available by ftp. A web calculator is here . C source code released under the GPL is here , in Visual Basic (courtesy Ian Billing) here .
Francisco Bernal has adapted the code to make a Windows version with an interactive map interface here . It comes with source code and a dll. 16bit version .
My favorite weather briefing links. (I open a collection of them in tabs, using the Mozilla browser. Try it. You'll like it, provided you have a fast Internet connection.
Some reading matter:
Some other files that may be of interest are available in my ftp directory
An (ex-) IFR student's checkride story.
Joe Campbell's IFR diary -in which I also feature!
Ed Williams is a 4200+ hr ATP-MEL Comm-SEL CFII. He owns a C182 based in Livermore CA. He developed and taught weekend ground schools for Aviation Seminars. He specializes in IFR instruction out of HWD and LVK.