The first DoubleVar (c_var) is assigned to the entry by specifying atextvariable property for it. This means that the entry will display what is in that DoubleVar, and if the value in the DoubleVar is changed, the field display will automatically update to show the new value. Also, when the user types something in the entry field, the value in the DoubleVar will change. Note that a new label of “deg F” has also been added.