[time.clock.hires]

namespace std::chrono { class high_resolution_clock { public: using rep = unspecified; using period = ratio<unspecified, unspecified>; using duration = chrono::duration<rep, period>; using time_point = chrono::time_point<unspecified, duration>; static constexpr bool is_steady = unspecified; static time_point now() noexcept; }; }

Objects of class high_resolution_clock represent clocks with the shortest tick period.

high_resolution_clock may be a synonym for system_clock or steady_clock.

29 Time library [time]

29.7 Clocks [time.clock]

29.7.8 Class high_resolution_clock [time.clock.hires]