# Classification using expression

Use expressions to calculate properties of individual classes in a category.

The last Expression can be `TRUE`

which will imply that the last expression will always be assigned if all above evaluates as false

## Parameters

### Expression

NOTE The expressions are applied in order top-down

Choose a new class and write the expression for it.

Click the “Add” button to add additional classification expressions. Click the color square to select color for the classification class.

The operators that can be used:

Standard arithmetic (`+`

,`-`

,`/`

,`*`

…) and comparison operators (`=`

,`>`

,`<`

…) as well as some mathematical expressions (…) and constant values can be used in expressions.

The parameters that can be used:

`Area`

`Length`

`Width`

`Circumference`

`Regularity`

`Roundness`

`Angle`

`D1`

`D2`

`X`

`Y`

`MaxBorderDistance`

`BoundingBoxArea`

For details on each available property see: Object properties Details

### Pretreatments

In button-up applied order ⬆️ , meaning **UV** is applied first then **Center** and so on.

**Savitzky-Golay****Derivative****SNV (Standard Normal Variate)****Logarithm****Center****UV (Unit Variance) scaling**

For more on each type of pretreatment see: Pretreatments