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{{Refimprove|date=February 2013}}
In [[electronics]], the '''form factor''' of an [[alternating current]] waveform (signal) is the ratio of the RMS ([[root mean square]]) value to the [[Average rectified value|average value]] (mathematical mean of [[absolute value]]s of all points on the waveform).<ref>{{cite web|last=Stutz|first=Michael|title=Measurement of AC Magnitude|url=http://www.allaboutcircuits.com/vol_2/chpt_1/3.html|work=BASIC AC THEORY|accessdate=30 May 2012}}</ref> It identifies the ratio of the [[direct current]] of equal power relative to the given alternating current. The former can also be defined as the direct current that will produce equivalent heat.<ref name=Dusza>{{cite book|last=Dusza|first=Jacek|title=Podstawy Miernictwa (Foundations of Measurement)|year=2002|publisher=Wydawnictwo Politechniki Warszawskiej|___location=Warszawa|isbn=83-7207-344-9|author2=Grażyna Gortat |author3=Antoni Leśniewski |pages=136–142,
== Calculating the form factor ==
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Digital AC measuring instruments are often built with specific waveforms in mind. For example, many digital AC multimeters are specifically scaled to display the RMS value of a sine wave. Since the RMS calculation can be difficult to achieve digitally, the absolute average is calculated instead and the result multiplied by the form factor of a sinusoid. This method will give less accurate readings for waveforms other than a sinewave.<ref>{{cite web|last=Tanuwijaya|first=Franky|title=True RMS vs AC Average Rectified Multimeter Readings when a Phase Cutting Speed Control is Used|url=http://www.escoglobal.com/resources/pdf/white-papers/True_G2.pdf|publisher=Esco Micro Pte Ltd|accessdate=2012-12-13}}</ref>
The squaring in RMS and the absolute value in ARV mean that both the values and the form factor are independent of the wave function's sign (and thus, the electrical signal's direction) at any point. For this reason, the form factor is the same for a direction-changing wave with a regular average of 0 and its fully rectified version.
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