+1 sessions
Median return +0.27%Completed observations: 32
- Middle 50%
- -1.07% … +2.56%
- Positive returns
- 53%
Zscaler · Sigma Moves
Closed-period price moves, measured against their own history. One engine. Five markets. No forecasts.
Latest closed period
Zscaler's latest move against its own history.
What happened afterwards
All history-qualified moves of at least 2.5σ. Results after the event are descriptive statistics, not trading instructions.
+7 sessions
Median return +2.35%Completed observations: 32
- Middle 50%
- -4.21% … +8.42%
- Positive returns
- 59%
+30 sessions
Median return +0.53%Completed observations: 32
- Middle 50%
- -10.28% … +22.02%
- Positive returns
- 53%
Every rare move, in context
Instrument: ZS (price return)
| Date | σ | Move | Observed rarity | +1 sessions | +7 sessions | +30 sessions |
|---|---|---|---|---|---|---|
| 3 Feb 2026 | -2.59σ | -6.26% | About once every 40 trading sessions31 comparable moves / 1,255 observations | -1.20% | -9.12% | -17.05% |
| 29 Jan 2026 | -2.91σ | -6.23% | About once every 52 trading sessions24 comparable moves / 1,255 observations | -0.31% | -15.18% | -23.36% |
| 26 Nov 2025 | -6.01σ | -13.03% | 4 times in 5 years4 comparable moves / 1,255 observations | -0.19% | -2.81% | -14.03% |
| 8 Oct 2025 | +3.78σ | +7.22% | About once every 157 trading sessions8 comparable moves / 1,255 observations | +0.42% | -4.35% | -7.03% |
| 7 Oct 2025 | -2.64σ | -4.09% | About once every 43 trading sessions29 comparable moves / 1,255 observations | +7.22% | +2.22% | +0.12% |
| 7 Aug 2025 | -3.46σ | -5.81% | About once every 74 trading sessions17 comparable moves / 1,255 observations | -1.03% | +1.66% | +7.99% |
| 10 Jul 2025 | -3.59σ | -6.42% | About once every 97 trading sessions13 comparable moves / 1,255 observations | -2.17% | -2.62% | -8.72% |
| 30 May 2025 | +4.20σ | +9.79% | About once every 179 trading sessions7 comparable moves / 1,256 observations | +6.34% | +8.08% | +4.79% |
| 9 Apr 2025 | +3.61σ | +14.17% | About once every 105 trading sessions12 comparable moves / 1,256 observations | -3.34% | -4.17% | +25.08% |
| 4 Apr 2025 | -3.11σ | -9.13% | About once every 70 trading sessions18 comparable moves / 1,256 observations | +3.08% | +17.16% | +44.60% |
| 3 Apr 2025 | -2.90σ | -7.16% | About once every 57 trading sessions22 comparable moves / 1,256 observations | -9.13% | +3.76% | +30.85% |
| 10 Mar 2025 | -2.94σ | -6.74% | About once every 60 trading sessions21 comparable moves / 1,256 observations | +2.40% | +4.76% | +0.94% |
| 28 Jan 2025 | +3.47σ | +7.03% | About once every 90 trading sessions14 comparable moves / 1,257 observations | -1.49% | -0.22% | -3.37% |
| 18 Dec 2024 | -3.04σ | -7.36% | About once every 63 trading sessions20 comparable moves / 1,258 observations | -1.34% | -1.38% | +9.72% |
| 4 Sep 2024 | -10.13σ | -18.67% | Not previously observed in 5 years0 comparable moves / 1,258 observations | +3.26% | +8.23% | +21.91% |
| 31 May 2024 | +3.70σ | +8.50% | About once every 105 trading sessions12 comparable moves / 1,259 observations | -0.55% | +10.41% | +19.51% |
| 30 May 2024 | -2.50σ | -4.70% | About once every 36 trading sessions35 comparable moves / 1,259 observations | +8.50% | +17.40% | +30.53% |
| 28 May 2024 | -2.61σ | -4.36% | About once every 47 trading sessions27 comparable moves / 1,259 observations | +0.13% | +9.00% | +19.35% |
| 21 Feb 2024 | -6.30σ | -14.10% | About once every 248 trading sessions5 comparable moves / 1,239 observations | +5.72% | +2.48% | -14.92% |
| 5 Feb 2024 | -2.50σ | -4.90% | About once every 37 trading sessions33 comparable moves / 1,228 observations | +1.15% | +9.14% | -15.86% |
| 2 Jan 2024 | -2.56σ | -4.15% | About once every 43 trading sessions28 comparable moves / 1,205 observations | -1.00% | +7.60% | +19.26% |
| 3 Oct 2023 | -2.51σ | -5.86% | About once every 37 trading sessions31 comparable moves / 1,143 observations | +2.42% | +12.67% | +23.52% |
| 10 Jul 2023 | +2.82σ | +7.75% | About once every 49 trading sessions22 comparable moves / 1,083 observations | -4.46% | +4.39% | -7.45% |
| 8 May 2023 | +6.42σ | +20.63% | 3 times in 4 years3 comparable moves / 1,041 observations | +1.97% | +10.05% | +34.22% |
| 25 Apr 2023 | -3.04σ | -8.29% | About once every 54 trading sessions19 comparable moves / 1,032 observations | +0.81% | -4.96% | +56.98% |
| 5 Apr 2023 | -2.65σ | -8.33% | About once every 44 trading sessions23 comparable moves / 1,019 observations | +2.41% | +4.23% | +22.37% |
| 3 Mar 2023 | -3.54σ | -11.10% | About once every 91 trading sessions11 comparable moves / 996 observations | +0.48% | -9.45% | -11.45% |
| 10 Nov 2022 | +3.09σ | +14.51% | About once every 54 trading sessions17 comparable moves / 920 observations | +6.81% | +2.10% | -18.28% |
| 9 Sep 2022 | +5.46σ | +21.88% | About once every 175 trading sessions5 comparable moves / 876 observations | +2.98% | -8.15% | -19.96% |
| 1 Sep 2022 | -2.71σ | -8.58% | About once every 48 trading sessions18 comparable moves / 871 observations | -0.31% | +24.49% | -7.05% |
| 10 Aug 2022 | +2.53σ | +10.40% | About once every 41 trading sessions21 comparable moves / 855 observations | -0.94% | -7.87% | -9.89% |
| 9 May 2022 | -2.51σ | -11.48% | About once every 38 trading sessions21 comparable moves / 791 observations | -1.83% | -16.33% | -2.60% |
The number has a method behind it
Sigma measures the size of a log return relative to volatility estimated before the period. Rarity is counted from actual historical standardized moves, not inferred from a normal distribution.
σt = ln(Ct / Ct−1) / vtvt ← t−1, t−2, …
Volatility adapts to the market regime with EWMA (λ = 0.94 for daily and weekly observations). Current-period returns are excluded. Each historical σ uses its own prior volatility.
Both directions count toward rarity. Reference history spans up to five years. A period with no prior exceedances is labelled unprecedented in the observed sample; it is never given an invented recurrence interval.
Stock observations use split-adjusted price returns, without dividend reinvestment. Commodities are explicitly labelled ETF price proxies; they do not represent spot commodity prices.
Questions behind the sigma
What does a 3σ move mean?
The period log return is three times the volatility estimated from earlier periods. Sigma is signed: negative for declines and positive for rises.
Why not calculate rarity from a normal distribution?
Market returns have heavy tails and changing volatility. We count actual past absolute sigma exceedances for the same instrument and period.
Does “once every 200 days” predict the next event?
No. It is the number of historical observed periods divided by comparable moves. Events can cluster and the market regime can change.
How much history is required?
At least three years of valid standardized observations, after a one-year volatility warm-up. This normally requires approximately four years of source history.
Are all instruments directly comparable?
The engine is shared, but each instrument has its own prices, calendar, volatility and reference sample. Commodity cards use explicitly labelled ETF proxies.
What happens on quiet days?
The page shows the largest covered standardized move, the complete rarity scale and recent records. Missing data is reported separately from market calm.
For information only. Historical observations are not investment advice and do not predict future moves. A rare move can be followed by another rare move.