# Computed Value

_How to add and configure a Computed Value field in the {{Notebook}}
Editor._

---

## What This Field Does

A Computed Value derives a number from an arithmetic expression over
other fields in the same form — for example, multiplying a mass field by
a count, or averaging two measurements. The generated value is read-only
for data collectors; they see the result but cannot edit it, and it
updates automatically as the fields it references change.

The field stays blank until every field its expression references has a
usable numeric value, so a partially filled form shows no result rather
than a misleading one.

## Adding the Field

To add this field, open the
[ADD A FIELD dialog](../shared-settings/adding-a-field.md), navigate to the **NUMBERS**
tab, and click the **Computed Field** card. Then click the **ADD FIELD**
button in the lower right.

```{screenshot} field-types-design/computed-value-01-add-field.png
:alt: Adding a Computed Value — the NUMBERS tab in the ADD A FIELD dialog
:align: right
:width: 100%
```

## Configuring the Field

Click the field's **grey header bar** to expand it and see its settings.
For an overview of the settings shared by all fields — including Label,
Helper Text, Field ID, and the field toolbar — see
[Field Identity](../shared-settings/field-identity.md) and
[Field Toolbar](../shared-settings/field-toolbar.md).

Give the field a meaningful Label, review the auto-populated
Field ID, and add any desired Helper Text.

```{screenshot} field-types-design/computed-value-02-configured.png
:alt: Computed Value configuration in the {{Notebook}} Editor
:align: right
:width: 100%
```

### Computed Value-Specific Settings

The Computed Value's key feature is the **Expression** text area, which
defines the generated value using arithmetic over field references. Each
referenced field is written by wrapping its Field ID in braces, e.g.
`{Wet-Soil-Mass-g} * {Number-of-Samples}`. Below the expression, a chip
is shown for each numeric field in the form; clicking a chip inserts that
field's reference, which avoids typing the Field ID by hand.

| Setting          | What It Does                                                                                                                                     |
| ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------------ |
| **Expression**   | A text area where you define the calculation using numbers, operators, and field references in single-brace syntax (e.g., `{Width} * {Height}`). |
| **Insert chips** | A chip for each numeric field in the form. Clicking one inserts its braced reference into the expression at the end.                             |

The expression supports:

- **Arithmetic** — addition, subtraction, multiplication, division and
  remainder (`+ - * / %`), with parentheses and a leading minus.
- **Comparisons and logic** — `>`, `<`, `>=`, `<=`, `==`, `!=`, and
  `&&` / `||`, which evaluate to 1 (true) or 0 (false).
- **Conditionals** — a ternary `condition ? ifTrue : ifFalse`, e.g.
  `{Depth} > 0 ? {Depth} * 12 : 0`.

Field references must be wrapped in braces so that Field IDs containing
characters such as hyphens (e.g. `{Wet-Soil-Mass-g}`) are read as a
single reference rather than as subtraction. All referenced fields must
be in the same form as the Computed Value, and only numeric fields can be
referenced. A Computed Value cannot reference another Computed Value or a
Templated String.

### Shared Field Options

Configure any of the shared field options as needed.

For settings shared across all field types — including Annotation,
Uncertainty, Conditions, Copy value to new records, and Display in child
records — see
[Field Options](../shared-settings/field-options.md).

## Tips

- **Use the field chips to build expressions** rather than typing Field
  IDs by hand. Clicking a chip inserts the exact braced reference, so you
  avoid typos and do not need to remember a field's ID.
- **The result stays blank until all referenced fields have values.**
  This is intentional — a partially complete record shows no value rather
  than a misleading partial calculation.
- **Reference fields by their Field ID, not their Label.** The Field ID
  is shown on each chip and is what goes inside the braces; it stays
  stable even if the field's Label is later changed.
- **Computed Values are read-only for data collectors.** They see the
  calculated result but cannot edit it, keeping the value consistent with
  its inputs.