A steady clock ticks at a uniform rate and cannot be adjusted. Its `is_steady` member is true; unlike `system_clock`, its `now()` value will not move backward because of clock adjustment. section 4.3.1
Use a steady clock for elapsed-time measurements and timeouts: a system-clock adjustment does not change the elapsed duration. A wait can still take longer than requested because of scheduling and clock precision. section 4.3.1 section 4.3.2
std::future<int> f=std::async(some_task);
if(f.wait_for(std::chrono::milliseconds(35))==std::future_status::ready)
do_something_with(f.get());
A 35-millisecond future wait illustrates duration-based waiting measured with a steady clock. section 4.3.2
