i might add...
we are compelled to be inside our assigned frequency allocations
so - knowing exactly where you are is a must
we use transmitted standards to calibrate our equipment
there are many such standard transmissions around the world
but, here in the US, it's the national institute of standards and technology
what used to be called the national bureau of standards
they transmit signals on 5, 10, 15, 20 MHz, as well as a few others
the transmitter carrier is phase-locked to an atomic clock - very accurate
besides the accurate carrier frequency, they transmit time information in voice, digital, morse
as well as propogation predictions and other stuff (condition of the ionosphere, etc)
because the time is "paired" with the frequency standard, hams are unnecessarily fascinated with having accurate clocks - lol
you are likely to see a ham's second hand roll over precisely when the beep happens ::)