Bob, stop for just a moment and THINK about what you just said. "When you click off a stopwatch at 10.50 seconds, you are halfway through the eleventh second." You are exactly right. At 0.50 seconds you were halfway through the first second, not the 0th second. You hadn't measured 10 seconds until the end of the tenth second. Now COUNT those 10.50 seconds you just clocked off on your stopwatch. The first second, the one that started at 0.00 and ended at 1.00, was the FIRST second. Second #1. Not second #0. There was no second #0. Second #1 started at 0.

You say there had to be a year that "started with zero." Every year starts at 0. Every day starts at zero. But the calendar has NO day numbered zero. The first day of year 2000 ended at the end of January 1st, not January 0th. Today is the 21st day of January. It's the first day of the third group of 10 days of this month. The first 10 days were January 1st through THE END OF January 10th.

Today is January 21st. Does that mean 21 days have already passed since the moment this year started at 0?.