Every receipt creates a cost layer at its purchase price. Issues consume the oldest layer first, then the next. When prices change, stock left in the store is valued at the most recent costs.
For a contractor or workshop, FIFO means a job card or project is charged the real cost of the spare part or material it used, not an average that hides price changes.
How Civova handles it
Civova creates a FIFO cost layer on every goods receipt and consumes the oldest layers first on every material issue, so stock can never go negative.