How do you calculate the sum of such virtual values?

[Uzo]

then you have to create relations to these numbers and rollup-sum these relations

How to sum up different amounts for each item?

you need to relate items to sold items, then use the rollup column to sum that relation [Screen Shot 2021-12-21 at 6.22.41 PM] [Screen Shot 2021-12-21 at 6.26.52 PM] remember… sum relation, not a lookup, I put lookup there just for better understanding what is in the sold sheet… you can also use this technique to count sold items, get average or range …