Abstract: A watermark embedding method includes the following steps. The input video signal is received by a processing circuit. Grayscale information of a watermark signal is generated by the processing circuit according to a time series data and a predetermined plane. During a dark sate and a bright state in each of a plurality of consecutive periods, phases of the time series data are opposite and integral values of the grayscales of the predetermined plane are the same. The processing circuit embeds the watermark signal into the input video signal to generate an output video signal with the watermark information. The display panel displays an image according to the output video signal.

Abstract: A screwdriver is equipped with a removable ring tab on which words or diagrams are provided. The screwdriver has a handle portion and a shank portion and on the handle portion is disposed a recessed groove in which the ring tab of a like or different color can be housed. The ends of the ring tab are provided with a retaining protrusion and a retaining cavity respectively for locking the ring tab in place. Words or diagrams of different sized can be printed or punched on the ring tab instead of on the handle portion whereby even mistakenly printed or punched words or diagrams can be easily removed by replacement of the ring tabs without discarding the whole screwdrivers in mass production. Besides, the printed or punched words or diagrams are not easily abraded away in long term operation.

Abstract: A knockdown hand tool structure. The structure includes a grip, a screwdriver stem, a fitting post and a socket. A front end of an elongated stem of the grip is formed with a central hexagonal fitting hole with a certain depth. A stop sleeve is fitted on the front end of the elongated stem. A steel ball and a compression spring are received in the stop sleeve. The screwdriver stem is a hexagonal stem body. Two ends of the screwdriver stem are respectively equipped with different specifications or patterns of screwdriver heads. Certain portions of the body of the screwdriver stem are formed with annular engaging grooves with V-shaped cross-section and a certain depth at equal intervals. The fitting post is a short cylindrical body.