4.6 Inventories
Fingrid prepares for outages by maintaining reserve power plants. The inventories contain fuel for reserve power plants, spare parts for submarine cables, back-up equipment and parts for substations, and repair equipment for transmission lines. The aim of stockpiling is to achieve sufficient preparedness in case of faults and events possibly occurring during times of crisis at the substations and on the transmission lines owned by Fingrid.
8. INVENTORIES, €1,000 2017 2016
Materials and consumables at 1 Jan    
Material stocks 6,836 6,144
Fuel stocks 6,412 5,995
Work in progress 281 131
Total 13,529 12,269

Accounting principles

Inventories are measured at the lower of acquisition cost or net realisable value. The acquisition cost is determined using the FIFO principle. The net realisable value is the estimated market price in normal business reduced by the estimated future costs of completing and estimated costs required by sale. Inventories consist of material and fuel inventories.