Product works as advertised and appears to show even the slightest increase in the levels as I tested by taking a few breaths of 95% compressed O2 and watched my level increase by 3% very shortly thereafter.

Works as advertised

Worked as advertised.

Can fast, works as advertised and came with batteries

It was broken as if someone stepped on it.

Works as it is supposed to

well I just think it's very cheaply made

The LED’s