# 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

#### Category

Choose which classification category to use.

#### Expression

NOTE The expressions are applied in order top-down

Choose a class from the category and write the expression for it.

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

Select any pretreatments to apply to the spectrum prior to expression evaluation, see Pretreatments