>?????
>>because the densest is max and then the densest gradient is 0
>>this minimize the error measure.
Imagine a curve that shows temperature on the horizontal scale, and density on the vertical scale.
At the temperature where water is densest (close to 4 degrees C), this curve has a horizontal slope. This means that a small change in temperature will result in a much smaller change in density than at some other temperature where the slope is not horizontal - for example, at 50 degrees. Therefore, measurement errors are reduced.
Difference in opinions hath cost many millions of lives: for instance, whether flesh be bread, or bread be flesh; whether whistling be a vice or a virtue; whether it be better to kiss a post, or throw it into the fire... (from Gulliver's Travels)