Diagnosis. Your doctor can often diagnose dehydration on the basis of physical signs and symptoms. If you're dehydrated, you're also likely to have low blood pressure, especially when moving from a lying to a standing position, a faster than normal heart rate and reduced blood flow to your extremities.
A Corporal is a noncommissioned officer, whereas a Specialist is not. Unlike other NCO ranks (such as Sergeant, Staff Sergeant, etc.), promotions to Corporal don't have to be DA approved (although they can be), since it's considered a lateral promotion, with no changes made to pay.
Ranks vary widely from town to town as do the functions of the rank. In some departments, a corporal might be a low level supervisor, in others a corporal might just be a rank for senior patrol officers that doesn't really give them any more authority. Many police departments use military ranks, mostly from the Army.