The Audio Line-Up Swither & Lead Kit has been designed to allow owners to easily carry out a line-up of their machines using a minimum of test equipment. 
Service manuals talk of dBs, using a DVM, "connecting the inputs in parallel" etc. What does that all mean? How do you know if the input level is right? And what the correct replay level is anyway? 
This kit is ideal for the owner who occasionally needs to line their machine up. It comprises a 3-input passive switch box, modified to allow you to check the level you are inputing from a pure tone source, using a simple RMS reading Digital Volt Meter (DVM) - any device that can generate a pure tone source any will work, even those from an app on a phone. The switch-box can then, in-turn, switch the DVM to monitor the two outputs to check the replay or record level. 
Loop throughs on the switch-box inputs and outputs allow feeds to a scope, for azimuth monitoring and adjustment, and to an audio amp etc, so you can hear what you are doing. 
The kit consists of the switch-box, a set of leads, instructions and an RMS to dB conversion chart. 
You will need a simple DVM, a tone source (PC, phone app or a simple bench unit), a dual-channel 'scope (a simple PC app, or a low-spec model will do) and a line-up tape, such as a those available from MRL.
This kit, and the associated items, is significantly cheaper than a dedicated audio test set and will end the fiddly plugging and re-plugging required when using test leads.