It is since, I ran a belt for years with A/C, A.I.R. PS, Alt, then another one same configuration. Now I'm running one w/o A.I.R. the size their book called for. It was the shorter one that lined up the marks perfectly but, like I said, that one jumped a groove each time I started it. Oh well.That is a strange one and my guess is just that, a guess. Have never seen a belt jump a groove unless there was an alignment problem with one or more pulleys.