[larard]

I have a ruler. What number does the first centimeter start at?

[hgomersall]

It's a bit like all those people claiming that the new millennium shouldn't have been celebrated until 2001. They didn't stop to think how many years pass between the epoch and the time of interest. You celebrate a baby's first birthday after one year of time has passed. Until that point they are zero (and a bit) years old.

[fluidcruft]

Do you typically measure sets with a ruler?

Furthermore it depends on what you're doing with that first centimeter. In many instances the first centimeter is correctly considered to be 0.5