code: function determineStepSize(min, max, unit, capacity) {
  	var range = max - min;
  	var interval = INTERVALS[unit];
  	var milliseconds = interval.size;
  	var steps = interval.steps;
  	var i, ilen, factor;
  
  	if (!steps) {
  		return Math.ceil(range / (capacity * milliseconds));
  	}
  
  	for (i = 0, ilen = steps.length; i < ilen; ++i) {
  		factor = steps[i];
  		if (Math.ceil(range / (milliseconds * factor)) <= capacity) {
  			break;
  		}
  	}
  
  	return factor;
  }
docs: Returns the number of unit to skip to be able to display up to `capacity` number of ticks
  in `unit` for the given `min` / `max` range and respecting the interval steps constraints.