@startuml

actor User
participant View
participant Presenter
database UnitDatabase
participant Unit

User -> View : Choose units & input value
View -> Presenter : Call convertUnits()
View <-- Presenter : Get user input
Presenter -> UnitDatabase : Send raw user input
Presenter <-- UnitDatabase : Return unit objects
Presenter -> Unit : Convert provided units
Presenter <-- Unit : Return converted value
View <-- Presenter : Return converted units
User <-- View : Show conversion output

@enduml