Today, I tried to measure the photoelectric effect with this PASCO device. PASCO ap-9369 http://physics.unr.edu/182labs/he Apparatus.pdf they now sell a new device, so I assume this one is no longer supported. The device is basically a black box. We have no idea what the circuit is inside there. All I know is it takes 2 nine volt batteries and has two banana output leads. Apparently, the device is supposed to output the stopping voltage. The literature with the device doesn't go into any detail of what's inside of the device. It's not mine, so I'd rather not pry it apart. We were getting pretty inconsistent data; the violet band produced a lower stopping voltage than the yellow band. Anyone use this device before? perhaps it is most advisable to pull it open if it's not working.