When I was a kid I built many radios, audio amplifiers, and digital circuits but quite often they did not work as expected.  I learned the hard way that taking measurements helps to understand the problems.  I have built many voltmeters, pulse generators, and oscilloscopes.  The culmination was a device I built around 1975, which is still in use.   

The "Messmoebel" (measurement furniture, named after the nice wooden enclosure)  contained an audio amplifier, a two channel, 10 MHz oscilloscope with input preamplifiers and time base, function generators (Wien Bridge and voltage controlled oscillator), and a multimeter. The power supplies generate 5 V and plus/minus variable Voltages ( 0 to 12 Volt).

Dual Channel Input and Preamplifier		X,Y Amplifiers and CRT
Power Supplies		The surrounding pictures show details of the preamplifiers, CRT circuits, and the power supplies.  Building the device from scratch meant hours of planning calculating, constructing the chassis, designing the printed circuit boards, getting all the electronic parts, soldering everything together, and making it work.  This was a very rewarding activity.  This device did its job for 30 years, it has worked better than all of the equipment the local High Schools had available for Physics lessons as my wife found out.
But that was then. Nowadays you can hook up a few integrated circuits to the parallel port of a personal computer, write a few lines of program in Visual Basic, and get a nice graphical user interface - GUI.  With a few mouse clicks you design a chain of pulses and an arbitrary wave form which is fed to a DAC.  An ADC takes analog measurements.   Now the results can be seen on the screen and printed in documents and sent over the internet.  This is less craftsmanship but with powerful computers fancy operations like Fourier Transforms and complex  image processing are available for the hobbyist.