I've been thinking about this for awhile. Earlier this year I sent an oil sample to Blackstone and it came back with much lower zddp additive concentrations than purported by the manufacturer and by a published independent report found online. I sent another sample to Oil Analyzers and that sample came back with concentrations matching both the manufacturer's claim and the independent test results. I emailed Blackstone about it and they said their lab equipment and results may differ from other labs. My question is why? I'm just trying to understand what would cause the discrepancy. Another additive level was off but I can't remember which one at the moment. I've read on this forum that it isn't uncommon for Blackstone to be off on certain additive concentrations.