Quantities change through Record change on the item's page, so the history shows when and why.
- Bought more — adds to the holding. Give the Price paid (total) for what you added and it is added to the cost.
- Sold some — reduces the holding, with an optional Sale price (total). Its cost is reduced in proportion.
- Sold all — records everything held on that date as sold. The item keeps its history and stops counting toward today's total; totals before that date still include it.
- Fix count — sets the quantity on a date without recording a trade, for when the number was simply wrong.
Each change has a date, so past totals and the value chart stay right.
When some was added without a price
If you buy more without entering a price, the recorded cost no longer covers the whole holding. The item is marked Partial cost and no gain is shown, rather than a misleading one. Edit the item and enter what everything held cost in total to complete it — or tick that the units added without a price cost nothing extra (a gift, or already included). See Cost and gain.