Fig. 6

Reference target with four grooves of varying depth and width. a Photograph depicting the (uncalibrated) reference target no. 513E, produced by Rubert & Co [41]. Expected groove depths (from left to right) are 1000, 500, 200 and \(30\,\upmu \hbox {m}\). b Hirox Nano Point Scanner (NPS) cross-section plot of the reference target. Blue line is the experimental NPS data. Orange dotted line is the fitted data, without non-affine artefacts. The boxes and their respective colours indicate the sampling locations for the results described in Table 4