In computing per diem allowances involving the international dateline, what factor is used?

When calculating per diem allowances that involve crossing the international dateline, the actual elapsed time is a crucial factor. This is because the international dateline represents a geographical boundary where the date changes, influencing how time zones and travel durations are calculated. Actual elapsed time reflects the total time spent on travel regardless of time zone changes, ensuring that an accurate accounting of travel days and associated expenses is maintained.

Using actual elapsed time allows for adjustments based on the specific circumstances of the journey, such as time spent traveling over the dateline. This provides a clear representation of the duration of the trip, which is essential for determining the correct per diem allowance to ensure that personnel are compensated fairly for their travel expenses. Other factors, such as estimated time or projected travel time, do not account for time zone changes fully, making them less reliable for per diem calculations in this context.