Draw a simple timeline marking every year from 2 BCE to 2 CE; you will see that because of the absence of a year zero, only 3 years have passed between those two dates.
The timeline from 2 BCE to 2 CE shows five years: 2 BCE, 1 BCE, 1 CE, 2 CE.
Because there is no year zero in the Gregorian calendar, the year 1 CE follows immediately after 1 BCE.
The total span is only 3 years: one year from 2 BCE to 1 BCE, one year from 1 BCE to 1 CE, and one year from 1 CE to 2 CE.
Explanation
The chapter explains on page 5 that 'In the Gregorian calendar, there is no 'year zero'. The year 1 CE follows immediately the year 1 BCE.' This is why when calculating years between BCE and CE dates, we must subtract 1 from the sum. The timeline visually demonstrates this concept.
Solution Steps
The timeline from 2 BCE to 2 CE shows the years: 2 BCE, 1 BCE, 1 CE, 2 CE
There is no year zero in the Gregorian calendar
The year 1 CE follows immediately after 1 BCE
The total span between 2 BCE and 2 CE is only 3 years