7. This screen shows a plot of SNR vs. time-of-day for the circuit from ARRL HQ (W1AW) to London. The chart shows two values for SNR. The black curve at the top is SNR in dB-Hz and its values are shown in the cursor hints. The lower black curve is SNR in dB for the bandwidth specified for the circuit. SNR is the primary measure of circuit quality and is used to define whether each band is "Open" or "Closed". Both predictions are interpolated to show values at five-minute intervals, and the blue flashing bar shows current time. The solid horizontal line shows the Required SNR level for the selected service type (SSB in this case), and the dashed line shows a level 10-dB below the solid line. Chart colors are green, yellow or red, depending on the value of predicted SNR with respect to the two lines. Most charts include "terminator bars" at the bottom, which show the condition of the circuit at each time-of-day. A light blue bar means that both ends of the circuit are in daylight; a dark blue bar indicates an all-nighttime path. Medium blue means that the day-night or night-day terminator (the twilight zone, or gray line) is passing over the path.