Technical Specification: Gregorian Calendar Arithmetic & Interval Calculations
Calculating the duration between calendar events requires rigorous adherence to astronomical models and time-measurement standards:
1. Millisecond Epoch Math vs Timezone Discontinuities
Simple timestamp subtraction can introduce insidious errors of ±1 hour caused by Daylight Saving Time (DST) transitions. Our calculation engine utilizes UTC normalized midnight timestamps (Date.UTC(y, m, d)) to ensure consistent 86,400,000 millisecond increments per solar day regardless of the client's local geographic timezone.
2. Business Days & Working Calendar Algorithm
Project management workflows require distinguishing between total calendar elapsed time and billable workdays. The algorithm traverses each day sequentially, evaluating the ISO 8601 weekday (where Monday is 1 and Sunday is 7) to categorize working days versus weekends.
3. Leap Year Rules (Gregorian Calendar Standard)
A year is a leap year if it is divisible by 4, except for century years (divisible by 100), which are only leap years if they are also divisible by 400. Thus, the year 2000 was a leap year, while 1900 and 2100 are common years consisting of 365 days.