Best way to check if RTC DS1307 is already setup?

Good morning

Thanks by your reply.
I think that second will start counting as soon we do rtc.start... otherwise seconds remains as 0... I Think...
There no exist other way?
I've tried looking the info (01/01/00 01 00:00:00 (MM/DD/YY DOW HH:MM:SS)) on datasheet but without success...

Thanks on advance
Best regards
Pedro Ferrer