The issue with digital meters is often the true RMS measurement of non sinewave AC voltages. Most of the late variable transformers vary the effective RMS voltage by chopping up the sinewave and the most inexpensive meters do not read that correctly. The usual method for inexpensive meters is to rectify the AC, store the peak voltage and scale that down by .707. So you can do that and display the result on a DC meter. But it will be somewhat inaccurate over the range of voltages measured. For our purposes, it's probably just fine. It will be repeatable and that matters most to us. The maximum voltage of about 18 VAC will be most accurate. I think that's the method Stan2004 uses in his post above.
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