0.5 years after his ostensible birth is a date within that first year: 30 June 1AD.
1.5 years after his birth is not within that “first year”; it is within the “second year”, or 2AD. Just like 1.5" is a measurement that falls within the “second inch” of a ruler.
That doesn’t make much sense though, year 0 does exist. We define our calendar based on Jesus’s supposed birth year, not his birth year+1. Or?
Year 0 doesn’t exist because it’s either before or after Christ being born. What would year 0 be?
There’d also be asymmetry if there was a 0 A.D. but no 0 B.C. (as that wouldn’t really make sense)
Yeah, year 0 doesn’t exist, it goes 1BC -> 1AD
Is 0.5" within the “first inch” of a ruler?
1AD is every date within the “first year”.
0.5 years after his ostensible birth is a date within that first year: 30 June 1AD.
1.5 years after his birth is not within that “first year”; it is within the “second year”, or 2AD. Just like 1.5" is a measurement that falls within the “second inch” of a ruler.
Only programmers start counting with 0. All the normal people start with 1.