A quick Google search returns many instances of the saying, “A man with a watch knows what time it is. A man with two watches is never sure.” The doubt implied by this saying extends to manufacturing plants: If you measure a product on two (supposedly identical) devices, and one measurement is in specification and the other out of specification, which is right?

The aforementioned doubt also extends to healthcare, where measurement data abound. As part of the management of asthma, I measure my peak expiratory flow rate (discussed below), and I now have two handheld peak flow meter devices. Are the two devices similar or dissimilar? How would I know? To see how I investigated this, and to see the outcome, read on. A postscript is included for those wanting to dig a bit deeper.

Background

In 2015, I was diagnosed with asthma, a chronic condition where the airways in the lungs can narrow and swell, making breathing more difficult. The worst of it occurred at my in-laws, where I experienced wheezing and had difficulty breathing. The cause? The family cat!

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