We present quantitative measurements of the scenario leading to chevrons in the dielectric range of ac driven electroconvection in a planarly aligned layer of the nematic liquid crystal Merck Phase 5. First, we demonstrate that the threshold of electroconvection is described correctly by the standard theory. Second, we characterize above threshold the appearance of chevrons out of the defect chaotic state by a rather sudden increase of the density of defects. Furthermore, we show that the

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... l correlations between defects characterizing the chevrons set in simultaneously. Finally, we give the onset curve of chevrons ͑voltage versus frequency͒ and also discuss briefly their further development.