Final answer:
A Soldier's Time in Service (TIS) is the total time they have served in the military, starting from the day of enlistment and including all active and inactive periods of service.
Step-by-step explanation:
The Soldier's Time in Service (TIS) refers to the total duration for which a soldier has served in the military. TIS is a crucial factor in determining various aspects of a military career, including eligibility for promotion, retirement benefits, and pay scale. Unlike the unpredictable nature of soldiers' actions on the battlefield as discussed in the provided information, TIS is a quantifiable and factual measure. For instance, during basic training, soldiers start accumulating their TIS, which continues throughout their period of active duty or reserve service. The calculation of TIS begins from the day a soldier enlists and typically includes all active and inactive periods of service.