Magellan MobileMapper CX Getting Started Guide - Page 80

English About Almanac Files When first using your MobileMapper CX, and because there is no recent almanac file available yet in the unit, the internal GPS receiver (or Mission Planning if used at that time) will use a default almanac file stored in its protected memory. After receiving GPS satellites for about 12 to 25 minutes, the internal GPS receiver will be able to create a new almanac file. This file will be stored in the "Windows" folder and named as follows: almyy.ddd Where alm indicates this is an almanac file yy are the last two digits of the year ("07" for 2007) ddd in the file extension represents the Julian day number (001 to 366). You can also store your own almanac files in the "Windows" folder using the same naming convention as the one described above. The internal GPS receiver and Mission planning will always use the most recent almanac file stored in the Windows folder. To force the use of a certain almanac file, rename this file (or rename the others) so that it can be seen as the most recent almanac. If you do that, don't forget to rename the files after use. Choosing the Appropriate Real-Time Correction Age Limit When selecting a DGPS mode, you have to set a parameter called Real-Time Correction Age Limit. Here are a few recommendations to help you set this parameter to the appropriate value. The default value is 2 minutes. This is a good value to work with in most cases. If for any reason, the reception of DGPS corrections is of poor quality, you can increase this time limit up to 10 minutes without significantly impairing the position accuracy normally achieved with DGPS. 72