Photogates are equipped with handy thumbscrews, and are easy to connect and reposition. Battery operated. Complete set includes Timer, two Photogates with cords, AC adaptor and user's manual. A very versatile photogate timer, Battery operated which allows to perform experiments without being connected to the outlet. There are five timing modes. Including interval mode which measure the time of interruption. Frequency mode which measure the frequency of regular interruption. period mode which measure the time between the first and third interruption count mode which keep track of the number of times the photogate beam is interrupted adaptor leads. it also works as a normal stopwatch. includes 9v battery and instructions. size 15 x15 x 6cm.