Čislitel'nye v nazvanijach mesjacev i dnej nedeli - Riekstiņš, Eduards 1919-1992 (Akad. Nauk Latvijskoj SSR, Inst. Fiziki, 1987)
PST: Numerals in the names of months and days in the week. - In kyrill. Schr. - Zsfassung in engl. Sprache