The Cursor value on the AQ7270 Optical Time Domain Reflectometer displays the level in dB that the signal is above the noise floor of the optical port you are connected to. The noise floor is basically the Dynamic range. This lets you know if you are approaching the maximum distance that you can test with the OTDR (Optical Time Domain Reflectometer). As the cursor value approaches zero the OTDR is nearing its maximum measurable distance due to the condition of the fiber optic cable. Please refer to the attached document for more details.