---
title: "head_circumference"
description: "The measurement of the longest distance around the head."
---

The measurement of the longest distance around the head.

**Purpose.** To record the measurement of the longest distance around the head.

## Source

| Model | Leg | Role |
|---|---|---|
| `openEHR-EHR-OBSERVATION.head_circumference.v1` | openEHR | defines this table |

## Columns

| Column | Type | Null | Description | Source |
|---|---|---|---|---|
| `id` | `uuid primary key` | no | Primary key. | — |
| `form_id` | `uuid` → [`form`](/docs/tables/form) | no | The form this entry was recorded on. | — |
| `form_block_id` | `uuid` | yes | The block within the form, when the entry is bound to one. | — |
| `event_type` | `text` | yes | null represents any_event | — |
| `head_circumference_magnitude`<br />`head_circumference_units` | quantity<br />`numeric`, `text` | yes | Head circumference | `/data[at0001]/events[at0010]/data[at0003]/items[at0004]` |
| `comment` | `text` | yes | Comment | `/data[at0001]/events[at0010]/data[at0003]/items[at0007]` |
| `confounding_factors` | `text` | yes | Confounding factors | `/data[at0001]/events[at0010]/state[at0008]/items[at0009]` |
| `device` | `uuid` | yes | Device | `/protocol[at0005]/items[at0006]` |

## Constraints

```sql
check ((head_circumference_magnitude is null and head_circumference_units is null) or (head_circumference_magnitude is not null and head_circumference_units is not null))
check (head_circumference_magnitude is null or (head_circumference_units = 'cm' and head_circumference_magnitude between 0 and 100) or (head_circumference_units = '[in_i]' and head_circumference_magnitude between 0 and 40))
```

## Unique

- `form_block_id`

## References

| Columns | Target | On delete |
|---|---|---|
| `form_id` | [`form`](/docs/tables/form) | cascade |
| `form_id, form_block_id` | [`form_block`](/docs/tables/form_block) | cascade |
| `device` | [`device`](/docs/tables/device) | no action |

## Indexes

- `head_circumference_form_id_idx` on `form_id`
- `head_circumference_device_idx` on `device`