Payment with debit card should not take more than 30 seconds.
Payment using any other method should take no longer than 2 minutes.
In case of a crash, system must boot up within 5 minutes.
Logging into system should not take more than 30 seconds. The log in screen appears immediately when someone tries to use it and it takes only entering username and password and pressing OK.
Usability
System should clearly show that something have run out.
When an error occurs, system must throw an understandable explanation and suggest a way of solving it.
System allows waiters to have many tabs at once, which means that some orders might be in parallel.
System should allow waiters to share their clients, when one waiter has too many clients at a time.
System must be able to display information about the whole order, including prices and notes about the every order per every person.