So just clarifying you could say to this question using the infromation everyone has given on vn :
Entity Principle
When a business disposes of an Asset (Sells) any of its remaining value (Residual Value) will be consumed by a separate entity. The depreciable value must be the value consumed by the business, so taking the difference between the purchase price (historical cost) and the sale price (residual value) keeps the entities of the company and the purchaser separate, hence adhering to the Entity Principle.
Reporting Period
Historical Cost – Residual Value determines the Cost Value that will be consumed to enable the Entity to generate future economic benefits from the Non-Current Asset. As the life of a Non-Current Asset is limited, it is reasonable to write part of its cost in each Reporting Period until it is sold or used up. There is also the expected benefit to come into the business in future Reporting Periods when the Asset is sold and the expected Residual Value is received.