Germany, 1923 airmail cover, Registered Printed Matter, Berlin to Riga. Mi # 235-37 mixed franking, tied by Berlin C 2 Luftpost CDS dated July 31, 1923. "Mit Luftpost" etiquette and Berlin 2 registed label. 
 
Back has Berlin C 2 Luftpost  CDS plus Riga arrival CDS dated August 3, 1923. Michel catalog 25 euros +.Good condition.