In this Chapter "wasting asset" means an asset with a predictable life not exceeding 50 years but so that—
In this Chapter "the residual or scrap value", in relation to a wasting asset, means the predictable value, if any, which the wasting asset will have at the end of its predictable life as estimated in accordance with this section.
The question what is the predictable life of an asset, and the question what is its predictable residual or scrap value at the end of that life, if any, shall, so far as those questions are not immediately answered by the nature of the asset, be taken, in relation to any disposal of the asset, as they were known or ascertainable at the time when the asset was acquired or provided by the person making the disposal.