The effects of tip tilt on measurement uncertainty in scanning probe microscopy and tip-shape calibration for inclined tip have been discussed. Uncertainty of the untouchable region is the essential component of measurement uncertainty. Tip tilt is one of the most important parameters to determine the uncertainty of the untouchable region. The presence of tip tilt deteriorates fidelity of images and precision of critical-dimension measurements. It is necessary to use equivalent tip for calibrating the dilation of feature by inclined tip. (C) 2004 American Vacuum Society.