<p><strong>Abstract.</strong> The Polar Cap (PC) indices were approved by the International Association for Geomagnetism and Aeronomy (IAGA) in 2013 and made available at the web portal <a href="http://pcindex.org" target="_blank">http://pcindex.org</a> holding prompt (real-time) as well as archival index values. The present note provides the first reported examination of the validity of the IAGA-endorsed method to generate real-time PC index values. It is demonstrated that features of the

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... ation procedure defined by Janzhura and Troshichev (2011) may cause considerable excursions in the real-time PC index values compared to the final index values. In examples based on occasional downloads of index values, the differences between real-time and final values of PC indices were found to exceed 3<span class="thinspace"></span>mV<span class="thinspace"></span>m⁻¹, which is a magnitude level that may indicate (or hide) strong magnetic storm activity.</p>