I used it for a while as an add and over quite a few vehicles (two 350's and one 4-cylinder), and never really came to any conclusions as to its efficacy. What I really wanted to see was some elevation in tbn, but never saw that either. It is a concentrated calcium carbonate in an ester base, or an "esterified calcium carbonate" concentrate in a PAO base fluid. Lately, I have concerned myself with the results of borate esters in engine oil and gear lube formulations, and less with the calcium adds. I have a techical paper that basically says if you use the concentrated calcium adds, the addition of borates into the basic mix greatly improves the calcium carbonate film deposition. IMO, we need more fleet testing to determine the efficacy of concentrated calcium adds. In other words, the jury, again IMO, is still out.