reck·on·ing 
(rĕkə-nĭng)
(rĕkə-nĭng)n.
1. The act of counting or computing.
2. An itemized bill or statement of a sum due.
3. A settlement of accounts: a day of reckoning.
4.
a. The act or process of calculating the position of a ship or an aircraft.
b. The position so calculated.