Validation

Validation over input fields can be activated either by clicking that field and then clicking elsewhere, or activating that page action (in calculator it is calculate, in shopping it is changing the stage).

If validation finds an error, that field will get a red border and a message will be displayed every time the mouse gets over that field. The message displays a short description of the error.

Some fields are just required to fill, others have exact rules on how to write the values.