Query on dep.

Dear Gurus,

Really I am confusing about depreciation. Please let me have idea on depreciation.

Usually in straight line dep. method dep. calculation will happen on useful life.

Ex:- Asset value-1000 USD

Useful life- 10 Years

Dep. per year- 1000/10=100 USD

Here no need to use dep. rates. Then why are we using dep. % and how this %'s will calculate dep.

I am very greatful to the peron who will clarifies my doubt.

Thanks in advance

NMB