std::chrono::duration_values::zero
From cppreference.com
                    
                                        
                    < cpp | chrono | duration values
                    
                                                            
                    | static constexpr Rep zero(); | ||
Returns a zero-length representation.
Parameters
(none)
Return value
returns Rep(0)
See also
| [static] | returns the special duration value zero (public static member function of std::chrono::duration) | 
| [static] | returns the smallest possible representation (public static member function) | 
| [static] | returns the largest possible representation (public static member function) |