Understanding Sexagesimal (Base-60) Arithmetic
Unlike our standard decimal base-10 numbering system, time arithmetic operates in sexagesimal (base-60). 60 seconds compose 1 minute, and 60 minutes compose 1 hour. This means standard decimal addition fails when computing time intervals—for instance, 1 hour 45 minutes + 1 hour 30 minutes does not equal 2.75 hours or 3.15 hours, but exactly 3 hours 15 minutes (or 3.25 decimal hours).
Frequently Asked Questions
How do I add hours and minutes together?
Add all minutes together, divide the sum by 60 to find the additional whole hours, and retain the remainder as minutes. Then add all hours together including the carry-over.
Why is time calculated in base-60 instead of base-10?
Time measurement originated with the ancient Sumerians and Babylonians around 2000 BCE, who used a sexagesimal (base-60) numbering system. 60 is highly divisible by 2, 3, 4, 5, 6, 10, 12, 15, 20, and 30, making fractional divisions easy.