Division Formula 7

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s_{\bar{η_{{EI}_{i}}}} = \frac{s_{η_{{EI}_{i}}}}{\sqrt{m}} = \sqrt{\frac{\sum_{m}^{j = 1} {(η_{{EI}_{i_{j}}} - \bar{η_{{EI}_{i}}})}^{2}}{m (m - 1)}}

The standard deviation of the efficiency value of the efficient alternator ( $s_{η_{EI}}$ ) is calculated in accordance with formula 8: