GPS coordinates - why S26.5 is not the same as S26 50'

Everyone and his dog now has a GPS, and very often businesses helpfully post their GPS coordinates so that potential customers can find them.  The problem comes in, however, when people do not realize that there are 60 seconds in a minute, and 60 minutes in a degree, and that depending on the format used in the particular GPS device, might be displayed in one of several formats.

Lets look at the coordinates for the London Bridge:
51° 30′ 29″ N, 0° 5′ 16″ W or 51° 30.4833 N, 0° 5.2666 W (Garmin default) or 51.508056, -0.087778


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If you mistakenly confused the formats, and posted the link as
51° 30.29 N,  0° 5.16 W:

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Fortunately the even worse error of:
51° 50′ 80″ N, 0° 8′ 77″ W is clearly wrong, and in such a case the original can be guessed.

In short, just as 0.5 hours = 30 minutes, 0.5 degrees = 30 minutes.
Safe navigating!