A friend told me.
In the technar kad studied the graduate work was - current straightener (well, it is easier to say from variable to constant and reduce the voltage from 220V to 6V). In general, the project is written a lot of schemes, a collection of experimental samples and so on. The block represented a box with 4 wires 2 in a socket 2 per voltmeter or elsewhere. By the way, it was hard enough to say, but nobody turned the winman. Everything worked well done.
Projects are stored for another 5 years. When the archives began to be decommissioned, they decided to find out if little of the details would be useful. And when disassembled by surprise, there were two wires on which the current was supplied were locked on the brick, the usual silicate brick, and at the output 4 batteries of 1.5 V)))