As I understand it, an add-on clock chip might be best assuming it is going to maintain accuracy, whereas some sort of internet based clock solution would obviously need a network connection. A gps based solution might work if only I knew anything about gps!
A GPS-based solution would need a "GPS mouse" which is basically a small puck containing the GPS receiver, that can be connected to a computer via a USB cable. The Pi would probably handle it automatically, and it would likely appear as a serial port to you - from which you periodically receive strings with location and time (if the GPS got a fix), similar to the one below:
RMC Recommended Minimum sentence C
123519 Fix taken at 12:35:19 UTC
A Status A=active or V=Void.
4807.038,N Latitude 48 deg 07.038' N
01131.000,E Longitude 11 deg 31.000' E
022.4 Speed over the ground in knots
084.4 Track angle in degrees True
230394 Date - 23rd of March 1994
003.1,W Magnetic Variation
*6A The checksum data, always begins with *
It has the advantage of not needing to ever be initialized thus working "out of the box" without special batteries and even after a complete power failure (and it might be fun to get accustomed with as a technology) but it's definitely not the cheaper solution (one can buy about half a fistful of RTC chips for the price of a GPS-receiver - anywhere from $40 to $90)
Bluenext USB GPS receivers, was £17 from EBay. Still trying to get it working on the Pi but works fine in Ubuntu.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
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