The tuner allows you to change expression and choice variable values using a slider. For expression variables, the slider's minimum, maximum and step correspond to the variable's minimum, maximum and step properties. To show an expression variable in the tuner set its constrain property to true, its minimum, maximum and step to valid values and the tune property to true. For a choice variable just set its tune property to true.
To show the tuner click the Tuner button in the Variables window.
For expression and choice variables click the plus and minus buttons to increase and decrease the variable value. Also click and drag the tuner handle or click anywhere on the tuner track to change the value. For expression variables edit the text fields to change the value or constraint of the variable. Hover the mouse over the variable name to show additional information about the variable.