Monotonic clock Vs Wall-Clock

I was trying to comprhend the difference between std::chrono::system_clock and std::chrono_steady_clock and I saw the term monotonic clock. That  triggered my attention.

Wall-Clock based on NTP(Network Time Protocol) time can be adjusting back or forward.

From UTC (leap seconds) or network delay, change DST( daylight saving time).

It gives real time of the world.

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Monotonic clock is a measurement of the time the system has been actively running since boot.

It is steady useful for calculate time interval.