Force curves. (A-B) Schematic illustrations. (C-F) Example data. The PZT retracted the cantilever base linearly to a preset position (B,C-F, red lines and right ordinate) and then held it there to stretch the molecules with a constant force (A,C-F, blue curves and left ordinate) to measure various times characteristic of molecular structural destabilization or rupture induced by this force. (C) A curve of 2 force drops (indicated by 2 in the first subscript of t_ij) and 2 periods at constant force (indicated by 1 and 2 in the second subscript of t_ij) with respective durations of time-to-destabilization t₂₁ and time-to-rupture t₂₂. Force drop triggered via feedback control further retraction of the PZT attempting to bring the force back to the preset level, which was successful after the first force drop by retracting a distance l_d but was unsuccessful after the second force drop even by long-distance retraction, indicating rupture. (D) A curve of 2 force drops but only 1 period at constant force with duration of t₂₁ but no t₂₂ resulting from premature rupture occurred before force was resumed to the preset level. (E) A curve of 2 force drops but only 1 period at constant force with duration of t₂₂ but no t₂₁ resulting from premature destabilization occurred before arriving at the preset force. (F) A curve of 1 force drop (indicated by 1 in the first subscript of t_ij, i, j = 1 or 2) and 1 period at constant force (indicated by 1 in the second subscript of t_ij) with duration of time-to-rupture t₁₁. Data shown were acquired by GPIbα-pulling, but those obtained by CR1-pulling were similar.