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Re: gps navigation
knots, if you've gotten rusty at it, I would say the one thing you need to be aware of is the choice of datums and co-ordinates. In theory all GPS charts in the US will be WGS84 datum and every GPS and program will be preset to match that. In practice? Especially with your older GPS that may have been switched, so never assume the chart and the GPS datum match.
Also, your GPS may be set up to display in DD.MM.SS format, or DD.MM.mm format, and sometimes you can't tell which. Make sure it is reading degrees-minutes-seconds, or all decimal degrees (there ISO engineering standard is simply degrees to five decimal places) or whatever everything can agree on.
As to how to use software or calculate distances and all that good stuff...well at least there, it is usually obvious if something is wrong. But the datum mismatch or format can really slip past you.
There are, or at least recently were, still parts of the US using the NAD27 datum, and if your chart is on that, your GPS can be off by 1/3 of a mile versus reality. Never assume the chart is right, just because the box makes it look precise.