A limited company follows the written down value method of depreciating machinery year after year due to

Comparability
Convenience
Consistency
None of these

The correct answer is C. Consistency.

The written down value method of depreciation is a method of calculating depreciation that takes into account the fact that the value of an asset decreases over time. The value of an asset is reduced each year by a fixed percentage of its original value. This method is used because it is consistent and easy to understand. It is also a fair method of calculating depreciation, as it takes into account the fact that the value of an asset decreases over time.

The other options are not correct. Comparability is not a reason for using the written down value method of depreciation. Convenience is not a reason for using the written down value method of depreciation. None of these is a reason for using the written down value method of depreciation.