Put another way, suppose you have trouble seeing objects at a distance and you can only see out to 20 ft what a person with normal vision can see out to 200 feet, then you have 20/200 vision. The 6/6 terminology is more commonly used in Europe and Australia, and represents the distance in metres.
1 SID, also s.i.d., is a veterinary abbreviation meaning to give medication once a day. 2  Medical professionals for humans instead use the term qd (an abbreviation for quaque die). 3  However, that term can be easily mistaken with the term qid (an abbreviation for quarter in die), which means four times a day.
A notation on a prescription that says q4h would mean every 4 hours. it stands for each or every q.o.d every other day q6hrs every 6 hours q.d. each day (from Latin quaque die) also Latin quater   Q or q on a prescription is shorthand for the Latin term quaque which means every.. So, qd or QD means every day and q4h or Q4H means every 4 hours..   Every.