Albeck, who was a religiously observant Jew, published a number of books in Hebrew and German on rabbinical literature, including "Introduction to the Mishna", "Studies in Baraita and Tosephta", "Introduction to the Talmuds", and others.
The Mishnat ha-Middot has nothing in common with the Baraita cited by the old scholars under that name: for the citations leave no doubt that the Baraita, even in its mathematical parts, was founded on the Bible; whereas the Mishnat ha-Middot is a purely secular work, and, possibly, it drew upon the same source as did Mohammed b. Musa, the oldest Arabic mathematician.
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The Baraita of the Forty-nine Rules (Hebrew: ברייתא מ"ט מדות) is a work of rabbinical literature which is no longer in existence except in references by later authorities. Rashi, the Tosafists, Abraham ibn Ezra, Yalḳut, and Asher ben Jehiel mention a work, "Baraita of the Forty-nine Rules," and make citations from it (thus, Rashi, ed. Berliner, on Ex. xxvi. 5; Yalḳ., Gen. 61, calls it "Midrash"; Rashi on Ex. xxvii. 6 calls it "Mishnah").
In order to accomplish this, he gathered all the relevant material from the whole Talmud Bavli, Talmud Yerushalmi, and all other Braysos etc., and presented them in chronological order in a sefer he called Sidrei Taharos on Maseches Keilim.
This assumption of Friedmann's was subsequently confirmed by the publication of a geonic responsum (A. Harkavy, Teshubot ha-Ge'onim, p. 107, No. 229, Berlin, 1888), where a baraita from the Sifre de-Be Rab to Exodus is quoted, which is the same passage as that cited by Naḥmanides from the Mekilta de-R. Shimon b. Yoḥai, in his commentary on Ex. xxii.
Other argue that he was an erudite in the Baraitas and Tosefta, which the latter also literally means an 'add on' or a 'supplement', and both are an 'add on' works to the classic texts, and in their view, this is the way he earned his known name.