If the Straight-Line depreciation method is chosen, why must the estimated life of the asset be accurately entered in an Asset Register Record? A business had purchased two vehicles couple of years ago, but both vehicles were sold on 1st February this year before this they reached their end of effective life. The vehicle A was sold off for a profit of $2000, but the vehicle B was sold at a loss of $1000. 

Record part of the journal entry for this event on the date of disposal, what amount and what side of the account should these amounts to be entered in either Loss on disposal or Gain on disposal?