Designed for repair II

Here's another example of a piece of test equipment designed for repair.

From gadgets

This is a painted brass plate from the rear of a signal generator. It shows the complete circuit diagram on the left and operating instructions on the right.   Of course it makes lots of assumptions - e.g. not everyone can read circuit diagrams,  and there were many perfectly good substitutes for the valves used.  The positions of valves are shown, but there's no indication of normal voltages to be found in the circuit - the easiest way of locating a fault.  Even so much better than is generally provided today.