I've done a lot of research, but I'm currently overwhelmed. The calculations I need to do are actually simple, such as: how many units of a product are in stock, how many orders exist for that product, or how many items were shipped in an order and how many are remaining. I'm developing an app that handles these calculations, but I'm unsure of the best way to implement these **calculated fields**. Should I use `property`, `signals`, or another method? I feel overwhelmed and lost. I would really appreciate it if you could explain the logic behind this and the correct approach, or provide some example code for similar operations.