The following two books by prof. Emanuel Tov are now available in electronic versions as modules with Accordance (macintosh, pc) together with search engines:
Textual Criticism of the Hebrew Bible (3rd ed., revised and expanded; Minneapolis: Fortress Press, 2012). liv + 481 pp. (incl. 32 plates). Electronic edition: Accordance, Oaktree Software, Inc.
The Text-Critical Use of the Septuagint in Biblical Research (Third Edition, Completely Revised and Enlarged; Winona Lake, IN: Eisenbrauns, 2015). Electronic edition: Accordance, Oaktree Software, Inc.