This paper describes a human machine interface approach focused on use by people with dementia. The core concept is that the interface is not visible, so the user believes they are performing the task undertaken without assistance, but the system will correct any non-completed or missed steps of the task. It also identifies abnormal operational steps which may indicate that the person is having difficulties so their carer should investigate. It is designed this way to address specific behavioral traits of persons with dementia. The interface has been tested by simulation and demonstrated ability to meet these requirements. The significance of this interface approach is that it can facilitates the introduction of automated devices into the person's home to help them undertake tasks but without creating new problems for themselves or others.