When a decoder does not function after it is installed, the problem may be the insertion of the data into the global cycle, the software, the encoder, or the distribution system. The decoder itself may be faulty, despite what testing indicates. Finding the problem can be difficult; it is made easier with test equipment, such as a data monitor. The data monitor deciphers incoming data and provides a readout. This includes general and box-specific data. By keying in an address, the operator can determine the authorization for the box with that address. The unit can flag changes in authorization and indicate which bits were changed. It can determine the length of the global cycle and count down the expected time until it is next addressed. It indicates whether there is a market number matches and whether it is authorized to decode. It flags parity errors. It also provides information about the signal itself, such as modulation depth, signal strength, absence of video, sync suppression level, and video inversion status.