Merv (Persian name: مرو sometimes transliterated Marw or Mary; , Mulu), formerly Achaemenid Satrapy of Margiana, and later Alexandria and Antiochia in Margiana (Greek: Αντιόχεια της Μαργιανήs) – in current-day Turkmenistan, was a major oasis-city in Central Asia, on the historical Silk Road, located near today's Mary. Several cities have existed on this site, which is significant for the interchange of culture and politics at a site of major strategic value. It is claimed that Merv was briefly the largest city in the world in the twelfth century http://geography.about.com/library/weekly/aa011201a.htm.

Minimum Efficiency Reporting Value is a rating of the effectiveness of air filters in removing particle contaminants from the air and is dependent upon the particle size.

The Minimum Efficiency Reporting Value is the standard comparison of the efficiency of an air filter. The MERV scale ranges from 1 (least efficient) to 16 (most efficient), and measures a filter's ability remove particles from 3 to 10 microns in size.

(Minimum Efficiency Reporting Value) A numerical system of rating filters based on a minimum particle size efficiency. A rating of 1 is least efficient; a 16 is the most efficient. See also ASHRAE 52.2.

a number from