Thunderstorms came through the area the night of September 12, 1999. You can see how the plot shows greater short-term variance while the storms were here. The time constant of the receiver is long enough to smooth these out greatly, but the meter needle still moves noticeably while the storms are around. Since the samples are made every 15 seconds, you see the result of a great deal of flux. Note the Monday day time outage on the transmitter signal.