html=>"50 Hz is a radio frequency in the SLF band used by submarine communication systems.<br>50 Hz is also an audible frequency which can be produced by double-bass, piano, and tuba.<br><a href='https://en.wikipedia.org/wiki/Musical_acoustics'>More at Wikipedia</a>",
html=>"1 kHz is a radio frequency in the ULF band used by mine cave communication systems.<br>1 kHz is also an audible frequency which can be produced by human voice, viola, violin, guitar, mandolin, banjo, piano, saxophone, flute, clarinet, and oboe.<br><a href='https://en.wikipedia.org/wiki/Musical_acoustics'>More at Wikipedia</a>",
html=>"1.00000099 MHz is a radio frequency in the MF band used by AM broadcasts, navigation systems, and ship-to-shore communication systems.<br><a href='https://en.wikipedia.org/wiki/Radio_spectrum'>More at Wikipedia</a>",