@dimitrios-kanellopoulos I would say that the intensity of the interval is controlled by a metric. This can be a scalar value or a range of two scalar values. Viewed this way, all work the same.
Put differently: people do intervals for a reason. For example, to get faster. In this example, the rationale is to go faster over a short period of time than you could over a long period of time. But what is faster? Listen to your body for the answer and correlate your feeling to a numeric value. Now that you have this value, you want your watch to assist you. So it would be nice if it told you if you are to slow (number too low) or to fast (number too high). And these conditions could be signaled visually, haptically or auditorily.