__________ method of depreciation calculation ensures that the interest is charged on the cost of machine asset every year on the book value, but the rate of depreciation remains constant every year.

ANS:B - Atraight line

It seems there might be a typo in your question, as "Atraight line" doesn't seem to be a recognized term. However, if you meant to refer to the "Straight Line" method of depreciation, I can explain that. The Straight Line method of depreciation is one of the most common and simplest techniques used for allocating the cost of an asset over its useful life. Here's how it works:

1. Initial Cost: Determine the initial cost of the asset, which includes not only the purchase price but also any additional costs incurred to get the asset ready for its intended use, such as delivery charges, installation costs, etc.
2. Estimated Useful Life: Estimate the useful life of the asset, which is the period over which the asset is expected to contribute to the company's operations. This could be based on factors such as wear and tear, technological obsolescence, or legal restrictions.
3. Residual Value: Determine the residual value of the asset, which is the estimated value of the asset at the end of its useful life. This is also sometimes referred to as salvage value or scrap value.
4. Annual Depreciation Expense: Calculate the annual depreciation expense using the following formula: Annual Depreciation Expense=Initial Cost−Residual ValueEstimated Useful LifeAnnual Depreciation Expense=Estimated Useful LifeInitial Cost−Residual Value​
5. Book Value: After each year, subtract the accumulated depreciation from the initial cost to determine the asset's book value at the end of each period.

The Straight Line method is called so because the depreciation expense is the same each year, resulting in a straight-line pattern when plotting the asset's book value over time. This method is easy to understand and apply, making it popular for financial reporting purposes and tax calculations. However, it may not accurately reflect the actual pattern of asset consumption or decline in value over time.