# Give fields units and write your first formula

> Give a number field a unit, add a Calculated field, write a formula that checks units, and see the result in both systems.

Source: https://www.speclatch.com/guide/units-formulas/write-a-formula
Who: Admin or Engineering. Plan: Every plan.
Last verified: 2026-11-11

## Before you start

- You need the Admin role, or Engineering with Confidential visibility: they add and change fields.
- You need a table. See [Create a table](/guide/tables/create-a-table). A few records with values make the preview useful.
- The example is a vertical sump pump table. **Setting depth** is entered in inches, and **Minimum pit depth** adds 6 in of clearance under it.

## Steps

1. Open **Fields** under **Data model** in the sidebar, and pick your table in the **Tables** list.
2. Click **Add field**, then the **Number** tile. Type the name `Setting depth`. The dialog's footer shows the key formulas use, `setting_depth`.
3. Under **Unit**, pick **in** in the Length group. The line below shows a sample in both systems, `1 in · 25.4 mm`, and **Change** picks other display units. Click **Create field**.

   ![The new Number field form with its Unit set to inches and a sample line showing the value in inches and millimeters.](https://www.speclatch.com/guide/units-formulas/write-a-formula-1.png)

   *Pick the unit you enter values in; the sample line shows both systems.*

4. Click **Add field** again and pick the **Calculated** tile. Name it `Minimum pit depth`.
5. In **Formula**, type `sett` and pick **Setting depth** from the list; its key goes into the formula. Finish it as `setting_depth + qty(6, "in")`. The **Insert** menu lists your fields, your functions, reference tables and math functions.
6. Read the line under the editor. Here it says **Returns Length · stored in**, followed by a unit; pick **in** if it shows another. A red message instead means the formula mixes kinds of value, and it says how to fix it.

   ![The Calculated field form with the pit depth formula, the line saying it returns a length stored in inches, and a preview table of results on real records.](https://www.speclatch.com/guide/units-formulas/write-a-formula-2.png)

   *The checker says what the formula returns; the preview shows it on real records.*

7. Click **Preview on real records** to check a few results, then **Create field**.

> **Numbers need units.** `setting_depth + 6` doesn't save: 6 is a plain number and setting depth is a length. `qty(6, "in")` makes it 6 inches. When inputs combine into a unit SpecLatch can't store, read each one with `num()` first.

## What happens after

SpecLatch computes the new field for every record in the table, and recomputes it when **Setting depth** changes. A pump with a 36 in setting depth shows 42 in, with a small ƒ beside it. Spec sheets print it as 42 in (1,067 mm). New fields start as Internal; the next article shows how to choose who sees them.