measures implied volatility, which is not directly observed but computed from an option's price using an assumed clock; this analysis counts calendar days while the market trades on business days; a zero-structure simulation containing no market behaviour at all -- constant true volatility, exact Black-76 prices on a random walk, no weekday effect planted -- reproduces this pattern's published effect almost exactly (simulated -1.25% vs published -1.97%) using only that calendar-day clock; and the effect weakens to insignificance (-1.97% to -0.45%, p 0.0001 to 0.067) under a trading-day clock, on the real data. Not tested -- not rejected on evidence.