Straight Line Method Depreciation

Depreciation policy is to charge it annually. If you need it monthly, dividing by 12 give the accurate measurement because systematic reduction of the asset is evenly spread. This is the meaning of SLM. 

You are correct. For example: 1000₹ asset which has five years useful life has 200 depreciation charge per annum. Then, 1000/(365*5)= 0.54794520547 depreciation charge per day. This is also same as 200 per annum. If a year has 261 working days, then depreciation= per day depreciation expense * 261= 143. The main aim of depreciation is to recover the cost of machine within its useful life. So, 200 is a recoverable amount which is better than 143 i.e., 200 tax will be reduced. It depends upon the depreciation policy and how useful life is assessed. If useful life is assessed based on the number of machine hours, then the useful life will increase beyond five years. However, there are other factors like rust, bad working environment like machine is over used in a day which will increase the wear and tear. The depreciation rates double if the machine is operated in double shifts. Finally, considering all of the above, tax authorities request companies to depreciate on an annual basis as per the Companies act 2013.