Steve,
When using split-coil transformers, or even multi-secondary coil transformers, the polarity is needed to be observed. If you were setting up a "Buck/Boost" transformer, this is especially serious, otherwise the results will not be correct.
On the kind of transformer shown here, the polarity would not be a serious issue to be known in the field - mainy since there's only one position and one coil.
Basically, there's no real crucial need to know [even understand] the polarity under normal circumstances in the field. It's nice to know this stuff, but not absolutely necessary.
When it comes to altering outputs via connection arrangements, then it becomes crucial for the installing person to understand how this is done.
To show how polarity can be found, my next series of schematics to be uploaded here will show the various techniques [that I know of] to find polarity. Testing equipment is simply a scalable volt meter [not as simple as a "wiggy", but a simple analog meter will work, along with a low cost DVM].
Hope this message covered your Q to your satisfaction
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Simply, this polarity stuff isn't important until the transformer is connected in a fashion that differs from it's "out-of-the-box" normal setup [like a Buck/Boost transformer]. That's when it's useful to know polarity.
Scott SET
