There are hundreds of incorrect ways to do Depreciation and only one correct way. When dealing with technology, the exact warranty period is a good depreciation period. When the argument comes up to depreciate a server over ten years, cut your losses and just record a statement against the purchase order.

What was the price then...

Working with complex business data requires that you have access to data. Very often systems lose or erase data that is old. The update of a price in a system my not detail the change or what range of time the old price was in effect. Temporal Data is best explained as weather data. Knowing what the average temperature of a day or month over the prior 5 years helps you predict when it is best to plant a crop or plan an event.