Loop makes a new glucose prediction every five minutes by computing the effects of insulin that has been administered from the pump, and carbohydrate records that have been entered into Loop. Two additional terms, glucose momentum, and optionally retrospective correction will also be used.
You can see the individual contributions of these effects by tapping on the predicted glucose graph on Loop's status screen.
This section needs to be fleshed out with details of how insulin and carb effects are calculated, and how momentum and retrospective correction work. For now, refer to: