For some adapters which I refer to as conversion-adapters, we could abstract out the conversion rate into a class of its own so that it becomes an inner-class which we can then maintain more easily and very importantly, more purposely.  By encapsulating this variance, we allow for easier maintenance.  In a code-based illustration of the odometer example, we abstract out the wheel into its own class and also abstract out the wheel-dimensions in a manner which allows us to update it.  This means that when we fit a new tire, the car’s computer will allow us to enter a new tire size.  It would automatically recalibrate the speedometer based on the tire size we fit.  This would ensure that the number of revolutions of the wheel is correctly converted to miles-driven/miles-per-hour.  We could think of this as a useful variation which we call the Calibrated-Adapter. By making the Adapter accessible from outside, we improve maintainability.