This is a concordance to the Septuagint, the Greek translation of the Old Testament used at the time of Christ. It offers the amazing opportunity of linking the OT & NT very nicely in your studies. I use this if I'm studying a NT Greek word/ doctrine, have traced it throughout the NT, and want to see examples in the Hebrew OT by checking if the same greek word was ever used to translate an OT passage by the 70 experts translators (who were brilliant in both languages at the time spoken) - hence common name "LXX" (commissioned by Alexander the Great?), just before the time of Christ.
You will need to be able to understand most of the greek letters since it does not have strong numbers or english translations. But for an advancing greek student, this one is gold. It is quite large and heavy, as I was told by Pastor Renaldo after he agreed to bring it to me in Zambia one year!
NOTE: After getting this tool, if you want to go even further, the next step is (for when you're looking at an OT Hebrew word/ passage/ doctrine & want to see all the ways it was translated in the Septuagint), to get the sequel.. the Hebrew/Aramaic Index to the Septuagint, keyed to the Hatch-Redpath concordance.