SNXX☆

A month’s return is its month-end close over the prior month-end’s, so a year’s figure is exactly the product of its twelve monthly cells — no separate annualisation, no resampling. A blank cell means no return exists for that month (the series had not started, or it is the very first month-end, which has nothing to be measured against). Blank is never zero.

Basis. SNXX is on the price only (split-adjusted close; dividends NOT included) basis, SPY on the total return (splits + dividends) basis. THE TWO DIFFER: one series includes dividends and the other does not, so the Δ column flatters whichever one is on the total-return basis. Read it with that in mind — the bases are printed rather than silently reconciled.

Partial years. A year marked “ytd” or “part” does not cover the full calendar year: either the stored history starts inside it (the figure is measured from the first month-end present) or the data stops before December (the figure runs through the last stored close). The row’s own tooltip names the exact boundary. It is never dressed up as a calendar-year return.

End of day. These are stored end-of-day closes, and the window is anchored on the LAST stored bar rather than today’s date — so the newest row ends where the data ends. Nothing here is intraday.