If I can remember correctly, the amplitude is the height of the wave (bottom to top measurement).
An easy (and probably a ridiculous) way to measure amplitude is to hook the device to a speaker.
For example, if you made a simple oscillator, and you want the approximate amplitude, hook it to a speaker, and then listen.
The louder the sound, the higher the amplitude.
If you don't want to use the speaker, then use an LED. The brighter the LED, the higher the amplitude.
As for exact measurements, since I'm a guy without many tools, I can't really help you for that one.