placing the monitor 10 and at the back of the plate 11 has an alcove 13 being covered by a cover 12 and the both side of the cover 12 has a left strip hole 121 and a right strip hole 122 further the main body 1 connects to a wire b 2 with a plug b 1 for electrically connecting to a machine 5 which provides a signal the alcove 13 comprises an upper room 131 and a lower room 132 at the middle and the upper and lower rooms 131 132 has a hole 1311 to fasten with a rod 14 by a screw blot a the side of alcove 13 has a first bar 133 at the upper and a second bar 134 at the bottom which is opposed to each other deposited and the alcove 13 has a cavity 135 neighbor up the first bar 133 an opening 136 at the middle a strip slot 137 opposed to the opening 136 which has a strip gear train 1371 and two spring rooms 138 139 at the bottom the top of the plate 11 has a concavity 111 extending a place 112 which has two pins 113 the positioning apparatus comprises a positioning member 22 a stop member 21 and a limited cover 23 the stop member 21 places in the place 112 of the main body 1 and has two limited holes 211 212 opposed to the pin 113 deposited and a beetle sheet 213 at the top for placing a button 214 and the side of the stop member 21 has a bevel beetle sheet 215 at the top and a third gear train 216 at the.