A method for controlling operation of a user control terminal of an agricultural machine, comprising - providing an agricultural machine having a tractor and an implement trailed by or carried on the tractor; - providing a user control terminal on the tractor, the user control terminal configured for receiving user input through a control knob; - operating the control knob in a first knob mode of operation, comprising - receiving a first function control user input through the control knob; - in response to the receiving, generating first function control signals for a functional element (10a; 10b) of the implement in a control unit functionally connected to the functional element (10a; 10b); - operating the functional element (10a; 10b) according to the first function control signals; - receiving a second function control user input through the control knob; - in response to the receiving, generating second function control signals for the functional element (10a; 10b) of the implement in the control unit; and - changing operation of the functional element (10a; 10b) for operating the functional element (10a; 10b) according to the second function control signals; characterized by - receiving a request user input for changing knob mode of operation for the control knob; and - in response to the receiving, operating the control knob in a second knob mode of operation, the user control terminal prevented from receiving function control user input through the control knob in the second knob mode of operation, comprising - displaying a user menu on a display of the user control terminal; - receiving a menu control user input through the control knob; and - controlling selection of a menu item in the user menu displayed according to the menu control user input. - providing an agricultural machine having a tractor and an implement trailed by or carried on the tractor; - providing a user control terminal on the tractor, the user control terminal configured for receiving user input through a control knob; - operating the control knob in a first knob mode of operation, comprising - receiving a first function control user input through the control knob; - in response to the receiving, generating first function control signals for a functional element (10a; 10b) of the implement in a control unit functionally connected to the functional element (10a; 10b); - operating the functional element (10a; 10b) according to the first function control signals; - receiving a second function control user input through the control knob; - in response to the receiving, generating second function control signals for the functional element (10a; 10b) of the implement in the control unit; and - changing operation of the functional element (10a; 10b) for operating the functional element (10a; 10b) according to the second function control signals; characterized by - receiving a first function control user input through the control knob; - in response to the receiving, generating first function control signals for a functional element (10a; 10b) of the implement in a control unit functionally connected to the functional element (10a; 10b); - operating the functional element (10a; 10b) according to the first function control signals; - receiving a second function control user input through the control knob; - in response to the receiving, generating second function control signals for the functional element (10a; 10b) of the implement in the control unit; and - changing operation of the functional element (10a; 10b) for operating the functional element (10a; 10b) according to the second function control signals; - receiving a request user input for changing knob mode of operation for the control knob; and - in response to the receiving, operating the control knob in a second knob mode of operation, the user control terminal prevented from receiving function control user input through the control knob in the second knob mode of operation, comprising - displaying a user menu on a display of the user control terminal; - receiving a menu control user input through the control knob; and - controlling selection of a menu item in the user menu displayed according to the menu control user input. - displaying a user menu on a display of the user control terminal; - receiving a menu control user input through the control knob; and - controlling selection of a menu item in the user menu displayed according to the menu control user input.