NIST has been working with different implementations of CD-AFM technology since the early 2000s and has experience characterizing the performance and uncertainties of three different CD-AFM instruments. One of the major goals of this effort has been the application of CD-AFMs as reference measurement systems for traceable dimensional metrology.35–37 The measurements described in this paper were primarily obtained on two CD-AFMs: (1) CD-AFM135 operates using a displacement measuring interferometer to detect the z-axis motion of the cantilever and (2) CD-AFM236 operates using a variation on the optical lever method to sense the cantilever motion. CD-AFM1 is thus capable of operating with lower vibration amplitudes than CD-AFM2. However, the larger cantilever vibration of CD-AFM2 means that it is potentially more robust against tip sticking. A logistical side note is that CD-AFM2 is not owned by NIST but belongs to a collaborating organization and is installed at their facility. However, its performance and uncertainties were characterized by NIST, and NIST personnel were permitted access to the instrument at the time of these measurements. Subsequent to our initial efforts, some results were also obtained using CD-AFM3, a newer instrument that is installed at NIST.37 CD-AFM3 has a more advanced tip control algorithm for scanning which can potentially reduce some imaging artifacts of CNT tips.