How to read the two formats
Latitude comes first and measures north or south of the equator. Longitude comes second and measures east or west of the prime meridian. In decimal degrees, a negative latitude means south and a negative longitude means west. A pair such as 51.500700, -0.124600 therefore describes a point north of the equator and west of the prime meridian.
Degrees, minutes, seconds (DMS) express the same point with compass directions. One degree contains 60 minutes, and one minute contains 60 seconds. This page converts the browser's decimal values into DMS in your browser. The two lines are different ways of writing one reading, not two independent measurements.
Precision and accuracy are different
The decimal pair is shown to six places so it is easy to paste into a map or message. The number of digits does not establish that the device knew its position to that precision. Use the browser's accuracy radius to judge how uncertain the point may be. A reading taken indoors or on a computer without strong location signals can cover a broad area even when its coordinates look detailed.
If the result seems wrong, try a place with a better view of the sky or better network reception and press the button again. Compare the map point with a landmark you can see. Our location accuracy guide explains common causes of errors. To send a point to someone else, read how to share your location and include the accuracy if it is wide.
Browser position and accuracy are defined by the Geolocation API and its accuracy property.