I checked some common commercial high-quality lab function generators and they seem to provide frequency output upto 50 Mhz (not a big deal), but with resolution of 1 uHz ! That means, they can generate signal with 50000000 Hz and also with 50000000.000001 Hz ?? That would equate to time-period difference of 4.00355*10^-22 seconds between those two signals!!! How can they possibly generate pulses with that high of time-resolution? Any idea?