Change Syntax from VDB( Number cost ; Number salvage ; Number life ; Number start-period ; Number end-period [ ; Number depreciation-factor = 2 [ ; Logical switch = FALSE() ] ] ) to VDB( Number cost ; Number salvage ; Number lifeTime ; Number startPeriod ; Number endPeriod [ ; Number declinationFactor = 2 [ ; Logical noSwitch = FALSE() ] ] ) for readability and to avoid misinterpretation of minus sign in start-period, end-period and declination-factor. Also, noSwitch instead of switch better names the logic used. Add Constraints: salvage < cost, lifeTime > 0, 0 ≤ startPeriod ≤ lifeTime, startPeriod ≤ endPeriod ≤ lifeTime, declinationFactor ≥ 0 and remove those from Semantics. Change Semantics to use the correct parameter names. Add math formula for integer periods and lifeTime? Mention interpolation for non-integer periods and lifeTime. Add to See also: SLN DDB: Add to Semantics: If period is an Integer number, the relation between DDB and VDB is DDB( cost ; salvage ; lifeTime ; period ; declinationFactor ) equals VDB( cost ; salvage ; lifeTime ; period - 1 ; period ; declinationFactor ; TRUE() ) Add to See also: VDB