"... The Septuagint on the Pentateuch contains a large number of words, phrases, clauses, and text units beyond the clause that do not match any corresponding element in the Masoretic text. On the other hand, many words, phrases, clauses, and larger text units found in the Masoretic are not represented by the Greek. Text units of MT lacking representation in LXX are considered 'minuses of LXX vis-a-vis MT,' whereas text units of LXX lacking correspondence in MT are considered 'pluses of LXX vis-a-vis MT' (in short: 'minuses' and 'pluses'). These definitions do not, in themselves, entail any judgment concerning the Hebrew source text reflected by the Septuagint. The possibility that the translator's version faithfully reflects a shorter/longer reading of the Hebrew source text is left open, as is the possibility that the translator has omitted or added a certain word, phrase or clause (intentionally or inadvertently). However, if the apparent differences between the Greek and MT obviously are related to translation technique, LXX in fact presents an adequate interpretation of the Hebrew as found in the MT, and cannot be regarded to contain either minus or plus. Hence, a 'plus' of the Greek possibly reflects a longer reading of the Vorlage, and a 'minus' possibly a shorter reading of the Hebrew ... for example Exodus 24:3, Genesis 31:16 ..."

Polak, Frank H. "Pluses and Minuses of the LXX on the Pentateuch Textual Transmission and Gradual Expansion" in Cook, Johann (ed.) Bible and Computer: The Stellenbosch AIBI-6 Conference : Proceedings of the Association Internationale Bible et Informatique, “From Alpha to Byte” (pp. 395-412) Brill, 2002