(current days): indicated by it's been used ... from... to (must be a point in time)

OK, so the date of the invention of the first clock is disputed among historians but it's agreed that the first method for telling the time was the movement of the sun across the sky. When the sun was directly ahead, it was midday and when it was on the horizon, it was early morning or early evening, according to whether it was in the east or the west. However, this method was problematic in terms of accuracy: but nevertheless, it's been used for countless years, from early humanity to --- .