DC potential drop has long been used for automatic crack length monitoring, yet details about its set‐up, causes of errors, precautions to achieve optimum performance and actual long term stability and accuracy under practical conditions have seldom been documented in detail. A DCPD system was established and details about its long term performance under varying loading and temperature parameters were evaluated. Necessary precautions to reduce error and improve accuracy are discussed. The system resolution is 0.003mm when applied to a compact tension specimen. The long term system accuracy achieved was ± 0.012mm. Two approaches for improvement were also attempted. It was found that the switch‐off approach at least doubled the accuracy and the reversing polarity approach raised the accuracy by nearly ten times. The improved system has been applied to a large pipe fracture specimen. The resulting empirical calibration data agrees closely with independently obtained finite element results.