# Expressions

In addition to `parameter`

, which defines the variables for a part, you can also use `variable`

. A variable is only used inside a part and are not exposed outside. Parameters are similar to arguments in functions in programming languages and variables are internal variables. In the object below we define a variable `b`

to set the size of a leaf. The variable is defined by an expression that includes a `random fraction`

function, wich can be found under the `math`

menu. A random fraction is a number between `0`

and `1`

like `0.12345`

. The random fraction is multiplied by 5 and then 4 is added. This means that the size of the leaf, variable `b`

will always between `4`

and `9`

. The leaf itself is create from a sphere that is scaled `0.5`

in X-direction to make it a bit flat. It is scaled in Z-direction to make it long. Another random expression is used to set a random turn around the Y-axis and Z-axis.

The `Palmtop`

object is included in a tree. The tree consists of a number of cones that are randomly rotated a between `-5`

and `5`

degrees. Note that every time that you generate the tree it will look a bit different.