# Performance curves

> Define a data series for a table, type each record's curve points, and let calculated lines draw themselves from the record's values.

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

One number can't describe how a pump performs across its range; a curve can. You describe the kind of curve once for a table, each record gets its own points, and charts, spec sheets and the portal draw them. Curves you can work out draw themselves on every record.

This guide defines a head–capacity series, types one pump's curve, then adds a calculated line.

## Series, curves and calculated lines

- A *series* is the kind of curve a table's records carry, such as Head–capacity: two axes, each with a label and a unit, and a tier.
- A *curve* is one set of points on one record, under a label such as *Maximum impeller*. A record can hold several per series, such as one per speed.
- A *calculated line* is a curve SpecLatch draws on every record, from that record's values or from one of its typed curves. Nobody types its points.

Points are stored in the series' units, so the axis units lock once any record holds typed points: changing them would rescale every curve.

## Before you start

- Defining a series takes the Admin role, or Engineering with Confidential visibility. Typing points takes Admin or Engineering.

## Define the series

1. Open **Fields** and pick the pump table.
2. Under *Data series (curves)*, click **Add series**.
3. Type the name *Head–capacity*; the key fills in.
4. Under *X axis*, type the label *Flow* and pick the unit *GPM*.
5. Under *Y axis*, type the label *Total head* and pick *ft*.
6. Under *Visibility*, pick who sees the curves. New series start as Internal.
7. Click **Create series**.

![The Data series (curves) table of a pump table, listing four series with their keys, axes and visibility; two carry a calculated-lines badge.](https://www.speclatch.com/guide/units-formulas/performance-curves-1.png)

*A series sets the axes, units and tier once for every record in the table.*

> **Tip:** For an axis without a unit, such as efficiency in percent, pick *None — plain numbers*.

## Type a record's curve

1. Open a Draft record of the pump table.
2. In its *Curves* section, click **Edit curves**. On a record you can't edit, the link reads **View curves**.
3. In the *Head–capacity* box, click **Add curve**.
4. Type the label *Maximum impeller*.
5. Type the first point in the units shown above the columns: *Flow* = 0, *Total head* = 104.
6. Click **Add point** and type the next one, such as *Flow* = 300, *Total head* = 100. The chart redraws as you type.
7. Click **Save curves**.

![The Head–capacity box on a draft pump's curves page, with a new curve labeled Maximum impeller, three points typed and the chart drawn above them.](https://www.speclatch.com/guide/units-formulas/performance-curves-2.png)

*Type points in the series' units; the chart follows as you type.*

## Draw a calculated line

A line has two ways to get its points:

- *Formula of x*: y is a formula of x and the record's fields. x runs evenly between two values, through a list, or through a reference table's rows.
- *From another curve*: each point of a typed curve on the same record maps to a new point, through one formula for x and one for y. Smaller impellers can come from the maximum impeller curve this way.

The example draws the standard motor's rating as a flat line on a power series, so the chart shows whether the pump stays under it.

1. On **Fields**, click **Edit series** on the power series' row.
2. Under *Calculated lines*, click **Add line**.
3. Type the label *Standard motor rating* and keep *Formula of x*.
4. Set *x runs* to *evenly from … to …*, and fill in from `0` to `max_flow` in `2` points.
5. After *y =*, type `std_motor_hp`, the motor's rating looked up from the linked motor.
6. When *Lines check out* shows, click **Preview on records** to check a few records.
7. Click **Save changes**. Every record in the table draws the line.

On a pump with `max_flow` = 169 GPM and a 10 HP standard motor, the line runs flat at 10 HP from 0 to 169 GPM.

![A pump's power chart with its typed maximum impeller curve and two calculated curves: a minimum impeller curve and a flat standard motor rating line, listed below the chart with their point counts.](https://www.speclatch.com/guide/units-formulas/performance-curves-3.png)

*Calculated curves come from the record's own values and carry an ƒ Calculated badge.*

## What happens after

Calculated curves redraw whenever the record's values change. Members whose visibility is below the series' tier don't see it, and the portal shows only Public series. When an Engineering member saves calculated lines, the series can't be more visible than the fields they read.