If the clock on your PC is wrong the code in the sketch won't work either.
Maximum accuracy can be obtained by using timeservers, however you need an ethernetshield. See - Arduino Playground - DS1307OfTheLogshieldByMeansOfNTP
If the clock on your PC is wrong the code in the sketch won't work either.
Maximum accuracy can be obtained by using timeservers, however you need an ethernetshield. See - Arduino Playground - DS1307OfTheLogshieldByMeansOfNTP