F21-E1B Function Characteristic1. With eight function buttons (6 single speed keys+1 beginning key+1 give up key). 2. Control contact is as much as 8. 3. With battery voltage warning device, the flexibility shipping is deliver to an end during low power. 4. Safety switch key's to stop from unauthorized user. 5. Program the button operate by means of means of notebook computer software. 6. Up/down, east/west, south/north can be programmed to interlock or non-interlock, toggle or normal etc. 7. Start button could be program to be start, normal, toggle operate etc.