A handheld computing device is used to copy files from the screen of a fixed computer. The method combines the calculation of optimum operating states with autonomy of the vehicle driver during braking. Chairs, methods of using chairs, and systems of chairs are also described. session identifications and portal storing means for storing session related information. The tripping unit includes a fuse configured to be connected in series to a main circuit of the circuit breaker and a detection unit connected in parallel with the fuse and configured to generate the tripping signal for the switching unit in response to the fuse being blown. When key data are generated from the key input device, a central processing unit may confirm whether a combination of the generated key data is identical to a predetermined character code, based on the key table stored in the flash memory.