> And yep, to preempt the inevitable comment: we used to have even more specialized devices, called "curve tracers", that were designed specifically for making V-I plots. They're more or less extinct now because SMUs can do the same job.

The ancient curve tracers, like the widely used Tektronix 576 or 577, could do things for which you would need much more expensive SMUs than that shown in TFA.

For example they could go up to voltages like 1500 V or 1600 V, to see the breakdowns of power transistors or diodes and they could apply very high powers during short pulses, e.g. up to 1000 W with the high current fixture, to see the V/I characteristics up to higher currents, like 200 A.

In general the most interesting parts of the V/I characteristics are towards higher voltages, to see the breakdown behavior, or towards higher currents, to see things like saturation voltages for bipolar transistors or minimum resistances for FETs and to see how the gain drops at higher currents.

A movie showing the use of a curve tracer:

https://youtu.be/bXbGktOHXzs

Nice pictures with the same:

https://www.pa4tim.nl/meetapparatuur/tektronix-576-de-koning...

> The book is meant for the inquiring hobbyist, including those who have tried to learn the craft and hit a wall before. With 420+ pages and 290+ meticulously-crafted color illustrations, The Secret Life of Circuits prioritizes modern problem-solving and true intuition over plumbing analogies or cryptic formulas.

IMHO this is a wasted opportunity to write a solid book on the subject. The poking at existing literature and offering a “true” intuition is tiresome at best.