# Tracking

Tracking measures the time an entity spends in each value of a discrete field: the duration of a refund in `pending`, the interval of a transaction between two steps, the elapsed time of an account under block.

Tracking is a capability of the field, not a separate kind of metric. When a [field is marked as trackable](/en/events/event_fields/#track-time-in-value), the platform starts recording every change of value per entity and provisions two derived fields, available like any other field of the event type:

| Derived field | Type | Content |
|---------------|------|---------|
| `Previous <field>` | dimension | value the entity was in before the change |
| `Time in previous <field>` | measure | duration of the most recently closed period |

## Closed periods

A closed period is measured with an ordinary metric: use an **Average**, **Maximum**, **Minimum**, or **Sum** aggregation over the `Time in previous <field>` field and group by the `Previous <field>` dimension.

The resulting metric expresses the latency of the process: the average time spent in each value and the longest period observed.

## Open periods

An open period has not closed yet: the entity remains in the value. The platform samples this set periodically and offers two measures:

| Measure | Content |
|---------|---------|
| Open count | number of entities currently in the value |
| Open time | age of the oldest entity still open |

The tracked field must have a fixed set of values (list or boolean), because each value is followed separately.

Without a filter on the tracked field, the metric follows every value, final ones included, whose count grows until the data expires. Filter the tracked field to follow only the relevant values.

### Restrict by open time

An open metric accepts an additional restriction, **Tracking scope**, which limits the count to entities open for longer than a given time.

The restriction distinguishes a stuck process from a slow entity. Without it, **Open count** includes entities that have just arrived at the value. With `more than 2 days`, the measure counts only the entities that exceeded the expected deadline.

The value must be lower than the tracking retention configured on the field. Below the given threshold, **Open time** records zero instead of the real age of the oldest entity.

The alert threshold is not part of the metric: it is configured as a condition on the [monitor](/en/behavioral/monitors/open_tracking/).

### Restrictions on open metrics

* An open measure supports only one grouping dimension. To break it down by more than one dimension, create one metric per dimension.
* The chosen dimension must be among the **breakdown dimensions** configured on the trackable field.
* An open measure cannot share a metric with ordinary measures.
* Breakdown dimensions added later apply only to entities entering the value from that moment on. Those already open remain without the breakdown until they change value.