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The Primi index is calculated in seven steps. Steps 1–5 produce the core index value. Steps 6–7 apply integrity filters that protect against manipulation and data silence.

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Step 1: Capture the current reference price

Every 15 minutes, collect the best bid and best ask from each eligible platform for each listed company. Apply staleness and sanity filters (see Data). Calculate the midpoint per platform, then average across all platforms with equal weight.
This produces a continuous composite price series updated throughout the day.

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Step 2: Capture the prior reference price

The rate of change is measured over a 60-day window. Both the current and prior reference prices are calculated as 7-day averages to produce a stable signal and prevent artificial index jumps caused by a single significant quote event entering or exiting the comparison window.
The 7-day averaging on each end smooths the signal.

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Step 3: Calculate the 60-day rate of change

This reflects the percentage change in the composite midpoint over the 60-day window — measuring momentum and trajectory rather than the absolute price level.

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Step 4: Calculate excess momentum against the historical baseline

The index does not measure the absolute rate of change — it measures whether the current rate of change exceeds or falls below the company’s own trailing 12-month average rate of change. This is the excess momentum signal.
When current momentum exceeds the baseline, the index rises. When it falls below the baseline, the index falls. When current momentum exactly matches the baseline, the index stays flat — regardless of whether the absolute price is still rising.

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Step 5: Express as an index or momentum price

Two representations of the same signal are available. Both update identically each day using the same excess momentum calculation. Index — launches at 100 for every company on their listing date:
Momentum price — launches at the composite midpoint on listing date, anchored to real secondary market data:
Both mean-revert toward their starting level when momentum returns to the historical baseline. The index is the official reference for derivatives contract settlement. The momentum price is the consumer-facing representation of the same signal.

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Step 6: Apply the anti-manipulation filter

Any quote movement that would shift the composite reference price by more than 10 percent within a single 15-minute interval is flagged and held for 48 hours. It is incorporated only if a subsequent independent quote or transaction on a different platform confirms the new price level. No single platform can move the composite meaningfully without confirmation from an independent source.

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Step 7: Apply momentum decay during market silence

If all eligible platforms simultaneously show no valid quote activity for more than 30 consecutive days, the index enters a decay state. During decay, the index drifts toward its neutral launch level at a rate of 0.1 percent per day. Index decay:
Price decay:
Decay stops immediately when any eligible platform resumes valid quote activity. It only triggers when all platforms are simultaneously stale — a single platform outage does not activate decay. The index decays toward the neutral launch level, not zero, because silence is a neutral signal, not a negative one.