C++11 chrono high_resolution_clock steadyness in busy loop?

The following code utilizes C++11 std::chrono to accumulate delta time between two subsequent ticks, and outputs the number of ticks accumulated for each second interval and the average tick time over this 1 second interval.

However, under my Xcode environment, when I run the code (in Debug), the outputs seem to be much longer than 1 second apart (likely at least 2 seconds apart) - it seems that the time line is extended longer than the actual time line.

If uncommenting the sleep line, the code exhibits the correct behavior.

Can anyone tell me what's going wrong?

#include <iostream>
#include <chrono>
#include <thread>

std::chrono::high_resolution_clock::time_point then{};

double accumulator = 0.0;
size_t count = 0;

void Tick()
{
    if (then != std::chrono::high_resolution_clock::time_point{}) {
        auto delta = std::chrono::duration<double>(std::chrono::high_resolution_clock::now() - then).count();
        accumulator += delta;
        ++count;
        while (accumulator >= 1.0) {
            std::cout << "count: " << count << " | average delta: " << 1.0 / count << std::endl;
            accumulator -= 1.0;
            count = 0;
        }
    } else {
        std::cout << "###" << std::endl;
    }
    then = std::chrono::high_resolution_clock::now();
}

int main(int argc, const char * argv[]) {
    // insert code here...
    std::cout << "Hello, World!\n";
    while (true) {
        Tick();

        // uncomment the following line exhibits the correct behavior
        //std::this_thread::sleep_for(std::chrono::milliseconds(1));
    }
    return 0;
}