OTDR gone wrong

This is the image of an OTDR trace when another engineer is measuring the same fiber from the other end of the fiber. Good practice would be to first test the fiber with a power meter, but the OTDR will normally indicate this also. If you start measuring at the same time, it is difficult for the OTDR to distinguish a live fiber signal from it’s own light, let alone the light of another OTDR! Of course, this was easily resolved by contacting the other engineer and deciding who got to go first 😉