1) In telecommunication signaling within a network or between networks, synchronous signals are those that occur at the same clock rate when all clocks are based on a single reference clock. (Plesiochronous signals are almost but not quite in synchronization and asynchronous signals are those that run from different clocks or at a different transition rate.)

What does it mean by 'based on a single reference clock'?? Can anybody explain?
https://whatis.techtarget.com/definition/synchronous

 

For example, I have ten computers that operate based on a single reference clock.
In other words, each of the ten computers can report the time of events with 10ns accuracy.
There is one quartz crystal oscillator that drives all ten computer clocks. This oscillator is the reference clock.

 

And if we have 1 input that records the data, 10 computers * 10nS, 1 computer has accucary of 100nS.