A method of frequency estimation for a GSM communications system is disclosed. At least one second seat with second control devices for a second operator is provided in the vehicle cabinthe driver’s cab in accordance with the invention, from which all of the essential driving andor operating functions of the utility vehicleconstruction machinery can likewise be controlled, including a steering function for the vehicle. When the access door is closed, the plunger retracts into and is stored in the access door. The drive control circuit can also be prevented from being affected by variations in potential of the output element or the like. The electrical connection assembly may be arranged to engage the connector responsive to movement of the battery pack in a direction substantially parallel to the direction of insertion of the battery pack into the battery compartment. A connection for connecting the mouthpiece to a breathing circuit is also provided which reduces the transfer of forces caused by movement therebetween.