
SeaMarks manual V. Additional Information •
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Calculation Method 1 uses each of the calibration waypoints to adjust the DMA table values near them to achieve
perfection. The influence of each calibration waypoints falls off with distance, so that distant ASF values will not get
adjusted as much. The influence extends to at least 40 miles. This procedure creates a user adjusted ASF file called
"ASFuser.bin" that contains the calibrated tables. Once the tables have been adjusted, the program recalculates all the
TD to LL conversions in the file using the new tables and uses the calibrated tables for all future conversions. To apply
the calibrated tables to other files previously converted with the old tables, open them and use Tools>Recalculate LL.
If you are using calculation method 3 for conversions, the government tables are ignored and a single ASF value is
applied across the whole area. For this, the average ASFs calculated above are used to recalculate all the conversions in
the file and the process is finished. No updates are made to the user-calibrated tables in this case. This method is useful
where the ASF do not vary much over the area in question and you only have calibration points in one small part of the
area. It is necessary to use this method if your data is outside the areas covered by the tables. The tables only cover the
North American continent, that is, coastal USA out to about 120 miles. They do not cover Canada, Central and South
America, Australia, Africa, Europe, or Asia. Below are the coverage areas for all the Loran chains covered by the
Defense Mapping Agency (DMA) tables.
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