Simply divide marked cable length by measured fiber length by to a known event. Figure A depicts the technique. A correction factor is critical to accurately locating breaks or components in long-length systems. This Applications Engineering Note (AE Note) addresses estimating cable length or event distance using an optical time domain reflectometer (OTDR). Contact the equipment supplier for unit-specific instructions or. This can be used for measuring loss of a length of fiber, where the OTDR will calculate the attenuation coefficient of the fiber, or the loss of a connector or splice. The calculation isn't a single formula, but rather an interpretation of the OTDR's displayed data.