unplanned depreciation in the first period

Hello,

There is one asset in use on this month, and cost is 10000, I input the unplanned depreciation is 3000 on this month,  so the NBV is 7000.

And I use the flat rate depreciation method for this asset, 20% on NBV,

When I run the depreciation of this month, the result of this is 2000=10000 *20%,  is it right?

I think this should be 7000 * 20% = 1400.  My deprecition method is based on the NBV , so why this is based on the cost instead of NBV ?

Hoping for your reply

Thanks