To convert a frequency to a channel number:

• Take the hundredths number in the frequency [i.e. in 72.990, use 99]
• Subtract 21 from this number [99 - 21 = 78]
• Divide by 2 [78 / 2 = 39]
• Add 21 to the result [39 + 21 = 60]
• The result is the channel number [60]

To convert a channel number to a frequency:

• Subtract 21 from the channel number [i.e. 60 - 21 = 39]
• Multiply the number by 2 [39 * 2 = 78]
• Add 21 to this number [78 + 21 = 99]
• The result can be found by prepending a "72." in front of this number [72.990]