I have set up an asset on sage with straight line depreciation of 2%

Cost price is £1,485.96, so depreciation should be £2.48 per month. However, when I enter NBV into sage of £1,218.49, it changes the depreciation to £2.44

But 1,485.96 x 2% / 12 = £2.48

Why is sage calculating something different? It says £2.44 until I put in net book value, but straight line depreciation shouldn't be affected by the NBV

Please help!

thanks

Clare