Grayline helps radio amateurs and shortwave listeners to benefit from "grayline propagation", a virtual line which divides the earth into the day and the night side. When one radio station is in the dusk and the opposite station is in the dawn, there is a possibility for so called "grayline propagation". At sunrise the D-layer builds up slowly and at sunset it disappears slowly again. During this change, low frequencies are not absorbed but refracted by the D-layer and enter the F-layer with a much lower wave angle than normal. In this way, longer distances can be used for propagation on the lower HF bands. "Grayline propagation&quot\; occurs in general from about 1.8 to 10 MHz, at which point the propagation paths are in the dark. The program lets you calculate possible "grayline propagation&quot\; paths for your location to other DXCC countries for any given date, enabling you to output the data to the screen or a text file.