With the current methods, the instrumental error in the measured hairpin length is 1-1.5 nm.  The length of a basepair, or 2 extended single-stranded nucleotides, is approximately 0.85 nm.  Therefore, the resolution of the system is at a few nucleotides.  The sources of noise arise from length-dependent Brownian motion of the bead anchored by the extended hairpin, statistical error in bead position determination, and slow mechanical drifts.  However, as mentioned earlier, such resolution is sufficient for the current sequencing method because changes in >4 nm are being measured.