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. Author manuscript; available in PMC: 2014 Jul 31.
Published in final edited form as: Nat Protoc. 2012 Apr 26;7(5):959–969. doi: 10.1038/nprot.2012.033

Figure 2.

Figure 2

Calibration of the reference needle. (a) Image of the reference needle. Scale bar, 5 mm. (b) A horse-shoe shaped weight (gray) is hung on the L-shaped tip of the reference needle to apply a load (P, nN). This results in the vertical displacement of the needle tip (xr, μm). The stiffness of the reference needle (kr) is determined by the slope of the load-displacement relationship obtained using several different weights. An example of a calibration data set is shown in (c) (see also Table 1 for description of the variables used.).