Hahaha...thank guy.good information,much understand.
I have info to share spk16.000G not in datasheets,SPK it's the manufacturer,but from the webite,I can't find the datasheets about this quartz crystal.
From other sources of quartz crystal manufacturers ,the lower ppm for quartz crystal is 10ppm frequency tolerance.
That good to build oscilator for timing like microsecond stopwatch,but if you
want more accurate timing,better we use OCXO(oven contro crystal oscillator) and more expensive oscillator
rubidium atomic clock.