how to read soviet style 3 digit bort numbers

topic title says it all pretty much…..I knowticed former warsaw pack countries & communist alligned countrys use 3 digit bort numbers on their ac and all are quite similar in layout

does anyone here know how to read them? from pics from different countries it seems the 2nd letter designates squadron or regiment? then last two aircraft number? 3** seems verry common for AC serials one can definatly see there is a system inplace, just what is it? laugh.gif

thanks in advance

Regards