An index is weighted by company size, and a small group of very large companies holds a large share of that weight. When the S&P 500 moves, those names account for much of it. Mega-cap concentration in SPY covers the arithmetic. What is new is that each of those names now has a perp, and the perps trade when the stocks do not.
The seven
NoVo follows the seven largest index names: NVDA, AAPL, MSFT, AMZN, GOOGL, META and TSLA. Each has a perp that trades around the clock. For each, NoVo takes the same measure it takes for the index perps: the perp’s price now against the perp’s own price at the last regular cash close. The method is the one in the implied open.
Narrow or broad
Set the seven beside the index perp and the shape of a move appears. If the index perp is lower and one name is far lower while the rest are flat, the move is narrow. It is one company’s news showing up in the index. If all seven are lower by similar amounts, the move is broad. Something is weighing on the whole market.
Those are different situations for anyone watching the index. A narrow move depends on one story. A broad one does not.
Unweighted, and why that matters
NoVo shows the seven unweighted, with the largest move first. That ordering answers which name moved most. It does not answer which name contributed most to the index. A smaller member can top the list with a big move and still account for less of the index change than a heavier member with a modest one. Read the list as a ranking of moves and keep the weights in mind.
When the names and the index disagree
Sometimes the seven are mostly higher and the index perp is flat. That says the rest of the index is offsetting them, or that the index perp and the single names are being traded by different crowds on thin books. Each perp is its own market with its own depth. Disagreement between them is a reading, and on a weekend it can also be noise.
Limits
Single-name perps are smaller than the index perps, and weekend depth is thin. A move on one of them can be a single order. Check open interest and volume before leaning on it. And the seven cover large companies only. No liquid perp exists on the Russell 2000 or IWM, so none of this says anything about small caps.
As with the index, each figure is a market price on another venue. It records what perp traders have done since the bell.
Where to see it
The Perps & Futures tab on Trader shows the index perps and the mega-cap perps together. While the cash market is shut, the seven are listed with their moves since the close. Index perps versus single-name perps covers how the two kinds differ.