Because the NMEA messages are likely from a buffered queue. No guarantee the queue is timed consistent from unit to unit. That's exactly why the 1PPS signal comes out of the GPS module, it is synchronized much tighter to GPS time, and could have jitter in the low nanoseconds. Sync your clock to the NMEA message, but adjust the timer according to the 1PPS signal. There is tons more published regarding this task, search the "time nuts" mailing list archive.

Thank you Gustavo for help, i will study and find the way for conversion. and post the result.

Magnifique

Hi Wilson, Thanks for taking interest in this project of mine.  Sorry, I don't have CAD schematics. However, I can make a decent fritzing sketch of it but I really have shortage of time. In fact when I did this project I did not even know of fritzing.  You have to wait for sometime till I get some free time to prepare it. Bera S  

Hi Loungdy, Thanks for taking interest in this old project of mine. Unfortunately, I don't have videos for this project.  However, if you go through the descriptions - it's pretty straight forward! Rgds. Bera