private float CalculateDifficulty(float length)
{
float perc = currentLength / gameLength;
float range = perc * perc * .5f;
float min = perc - range;
float max = perc + range;
if (min < 0f)
min = 0f;
if (max > 1f)
max = 1f;
float difficulty = Random.Range(min, max);
//Debug.Log ("diff: " + difficulty + ", perc: " + perc + ", range: " + range);
return difficulty;
}