how to undersand the following code about "std::chrono"?

auto elapsed_time = std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::high_resolution_clock::now() - start_time).count() * .001;

std::cout << taskname << ": " << elapsed_time << " ms / " << 1.0 / (elapsed_time * .001) << " fps" << std::endl;

why does the programer make the code so complicated, instead of a direct approach?