  Further improvements are made to the non-linear data analysis algorithm for
the atomic force microscope [P. Attard, arXiv:1212.3019v2 (2012)]. The
algorithm is required when there is curvature in the compliance region due to
photo-diode non-linearity. Results are obtained for the hydrodynamic drainage
force, for three surfaces: hydrophilic silica (symmetric, Si-Si), hydrophobic
dichlorodimethylsilane (symmetric, DCDMS-DCDMS), and hydrophobic
octadecyltrichlorosilane (asymmetric, Si-OTS). The drainage force was measured
in the viscous liquid di-n-octylphthalate. The slip-lengths are found to be 3nm
for Si, 2nm for DCDMS, and 2nm for OTS, with an uncertainty on the order of a
nanometer. These slip lengths are a factor of 4--15 times smaller than those
obtained from previous analysis of the same raw data [L. Zhu et al., Langmuir,
27, 6712 (2011). Ibid, 28, 7768 (2012)].
