This is the inductance test to determine if a mike cable is sensitive to coiling. This graph is inductance of the twisted pair. The min/max refers to the meter reading range due to noise and meter resolution. As frequency goes higher, the readings stabilize. In the 20 to about 200 hz range, the red and blue are the highest and lowest readings the meter gave due to noise, so don't assume either is correct, this is an error band. I missed a few datapoints, excel will not draw a line between them. I also inserted a 4 inch dia 4 inch tall cylinder of stainless in the coil, there was no change in readings, indicating zero solenoidal field. BTW, where the lines coincide, the actual values are identical coiled vs straight to between 4 and 5 digits.