Depreciation as per sch iii

Dear Professional,

I have A Doubt in Depreciation as per Sch II.If i purchased a computer on 01.07.2014 for Rs.10000.Deprecation rate 1-(500/10000)1/3=0.63

Depreciation till life of asset

2014-15      10000*0.63*270/360=4725

2015-16      (10000-4725)*0.63=3323.25

2016-17       (10000-4725-3323.25)*0.63=1229.6

2017-18      (10000-4725-3323.25-1229.6)*0.63*90/360=113.74

Residual Value=10000-4725-3323.3-1229.6-113.74

                         =608.41

Residual Value has to come Rs.500 by applying above rate but it came to to 608. what is wroung in this calculation?