The Maximum Usable Frequency for slip-distances of 750 km (MUF750) is the highest frequency that permits acceptable operation of a HF radio-communication service. The blue dots represent the MUF750 calculations based on observations from the digital ionosonde in Juliusruh (54.6°N / 13.4°E), Germany. The red graph represents the running polynomial one-hour forecast estimate of MUF750. The blue curves are the 90% statistical prediction intervals, and the orange intervals (if any) in the bottom of the plot show periods of no measurements.