17. ACE-HF presents a traditional HF MUF chart in this separate graph. The MUF chart updates automatically whenever a circuit change is made. The MUF curves give Maximum Usable Frequency predictions vs. time-of-day. The blue curve is the median of the daily Maximum Observed Frequencies (MOFs) over all days of the month at a given hour. The red HPF (Highest Possible Frequency) curve gives values expected only 10% of the time, and the FOT (Frequency of Optimum Traffic) green values are defined as the frequencies where the MOFs will be higher on at least 90% of the days of the month. The MUF chart has a blue flashing line to indicate current time, and horizontal lines showing the frequencies assigned to each band. MUF predictions give a measure of ionospheric conditions but do not account for other circuit variables such as atmospheric and man-made noise or antenna gain. MUF curves are another tool for predicting best frequency operation, but the SNR Summary Chart remains as the most accurate measure of circuit quality.