Thank you, @foothilla, for your clarifications. I confess that I don't know whether a dual-action (what I assume you mean by "bi-flex" -- new term for me) truss rod is the norm or not with instruments today. I assumed that it was (at least in non-Fender-type instruments), but, on reflection, perhaps without much supporting evidence. For what it's worth, I like my necks fairly close to flat -- I do like a little relief in there, but not, I think, much. It'll vary with the bass and the strings used, but, adjusting both relief and action by feel, I've historically ended up at least in the ballpark of Fender spec. Used to be on the low side but, like Janek Gwizdala, I've raised it a little in recent years.