Estonia 1993 Unique Final Day Cover "Bye-bye ruble!" FDC last day of circulation of stamps denominated in rubles

The unique item of the Last Day is dated 06/30/1993 - the last day of postal circulation of Estonian stamps, the denominations of which are indicated in Soviet rubles. Sending a Registered letter from Estonia to Finland by airmail is paid exactly at the rate of 3 Estonian kroons (exchange rate 10 rubles = 1 kroon). At the same time, the envelope contains the complete (!) first set of stamps from 1991, additional stamps with a letter designation (pp R, X, Z) and one stamp in the new currency 60s. A unique letter - a diamond in any Estonian chronology collection! Witness of the era, artifact