Field help (RATCUM) 

Calculated value, it cannot be entered. This is the total of the monthly rates or of the rates by annuity entered in the Depreciation rate table.
If the rate application mode is Rate by annuity and the Depreciation basis type has the value Balance sheet value - residual value or Balance sheet value, the following check is carried out: the sum of the entered rates augmented by the exceptional depreciation rate cannot exceed 100%.