Teach my child: How to use a clamp meter to measure AC current of electric heater

I have used electric multi-meter for many year (perhaps since I was a junior high school student)

This is the first time I buy and use a clamp meter.

Figure 1  Got the batteries installed

Figure 2  A electric heater (1200 W) was connected to a self-made extension cord (I made it two years ago). The cord was consisted with two strains of wires (the hot and ground wires), and I separated them. Clamped one strain of the cord and measured the AC current.

Figure 3  Yes! the cute palms with red sleeves were my boy's hands!

After measuring, I confirmed that the heater was not always running with the maximum output (every night, we could hear "click" sounds from the heater ever 10 -20 seconds, and my wife thought that really noisy in the night).

From the clamp meter, I also the current changed from  8.5 - 9.0 A to 0.2 A about every 10 sec.  This is the noise come from.

I just guess that the switching sound is using a thermo-switch to prevent the device overheating.

In addition, I think the life skills are more important than any grades of subjects in the school. Thus I taught my child how to measure AC current, even he did not know what was he doing!


References
Fluke AC/DC clamp meter manual (in PDF)
Electrical wiring in North America - Wikipedia