Constant Error
A constant error is an average of the errors over the range of all data. The x value will be independent of the y value. For example, an affixed scale will always have deviation from the zero setting whether the item being weighed is 100 lbs., 600 lbs. or anywhere in between and this error has nothing to do with the actual weight of the object. The average deviation of a single instance will decrease as the number of instances increases.