We are using "#47" pilot light bulbs (6.3V, 0.15 Amp).

When you are done making measurements, we need to measure the length of the filament.

Carefully break the bulb, snip off the filament (with two handles), and stretch it out.

Because you can still see the sinusoidal coils, you know that the following filament is not yet fully stretched.

Also, this filament broke near each handle while it was being stretched.