A method and apparatus are provided of characterizing a re-entrant SPM probe tip (30) through a single scan of a characterizer, thus dramatically increasing throughput, accuracy, and repeatability when compared to prior known tip characterization techniques. The characterizer also preferably is one whose dimensions can be known with a high level of certainty in order to maximize characterization accuracy. These dimensions are also preferably very stable or, if unstable, change catastrophically rather than in a manner that is difficult or impossible to detect. A carbon nanotube (CNT), preferably a single walled carbon nanotube (SWCNT), has been found to be well-suited for this purpose. Multi-walled carbon nanotubes (MWCNTs) (130) and other structures may also suffice for this purpose. Also provided are a method and apparatus for monitoring the integrity of a CNT.