I recently added the website of BruceAir, LLC (BruceAir.com) to my list of favorites. Bruce is a frequent poster on one of the flying forums that I read. If you have some time, please check out the wealth of information Bruce provides on many subjects.
I found the following links through the BruceAir website that took me to the FAA GNSS Library Fact Sheets. Here are two good reads for instrument pilots, if not to learn something new then a good refresher as spring time flying approaches.