BBW tells you the size. STD tells you the speed.
Most traders know Bollinger Bands. The bands widen when volatility is high, tighten when it is low. Bollinger Band Width quantifies that — how wide the channel is right now relative to its midpoint.
Standard deviation measures something different. Not the width of the channel — the velocity at which that width is changing. A market can have wide bands and be moving slowly inside them. A market can have narrow bands and suddenly accelerate with force. STD expansion catches that acceleration regardless of where the bands currently sit.
The Purple Bishop fires on that acceleration. When the 9-period rolling standard deviation doubles relative to where it was 5 bars ago, the Bishop appears. The market has not just moved — it has shifted into a higher-force regime. Something changed.
What standard deviation actually measures
Standard deviation measures how far individual bars are dispersing from their recent average. When bars are tight and overlapping — small candles, contained range — standard deviation is low. When bars start printing with more distance from each other and from the mean, standard deviation rises.
The key word is dispersion. Standard deviation does not care if bars are going up or down. It cares about how far they are traveling from the center. A violent move down and a violent move up register identically. Both are dispersing from the mean with force.
This is why the Purple Bishop carries no color from the ♛Queen. Direction is irrelevant to dispersion. The Bishop is telling you force is present — the Queen is telling you which way that force is pointed.
Why velocity matters more than level
A high standard deviation in a trending market is expected. The bars are large because the market is moving. That is not a signal — it is a description of what is already happening.
What is a signal is the transition. A market that has been moving with small, contained bars and suddenly prints two or three bars with significantly more range — that transition is the Purple Bishop. The STD did not just grow. It doubled in 5 bars. The character of the session changed in a few minutes.
This is what separates STD expansion from BBW expansion. The ♝Red or Green Bishop fires when the band width doubles — a level comparison. The Purple Bishop fires when dispersion velocity doubles — a rate-of-change comparison. They often appear together. When they do, the signal carries more weight.
Independent of the Queen — and why that matters
The ♝Red and Green Bishops require the Queen to be on side before they fire. Direction must be declared for the expansion to count as aligned. The Purple Bishop has no such requirement.
This independence is information. A Purple Bishop firing while the Queen is neutral — during a period of structural indecision — means dispersion is accelerating without a declared side. That is the market beginning to choose. Watch for the Queen to fire shortly after. When it does, the STD expansion was the warning that the decision was imminent.
A Purple Bishop firing with the Queen already on side is a different reading. The direction is known, and dispersion is now accelerating in that context. The move is gaining force. That combination — Queen declared, STD doubling — is one of the stronger confirmations on the chart.
Why it matters for options
Standard deviation and implied volatility are close cousins. IV is the market's forward expectation of dispersion. When realized dispersion accelerates sharply — STD doubling in 5 bars — the options market takes notice. Premiums adjust. Market makers widen spreads. The cost of protection rises.
For options traders, the Purple Bishop is a repricing warning. When it fires ahead of the ♝Red or Green Bishop, it often precedes the IV expansion that makes existing positions more valuable and new entries more expensive. The trader positioned before the Purple Bishop — during the ♝Yellow Bishop's compression — is watching the market catch up to what they already knew was coming.
On any chart
Standard deviation is available on every major charting platform. Add a 9-period standard deviation indicator to the sub-pane. Watch for sharp spikes upward — not a gradual rise, but a near-vertical acceleration from a base. That spike is the Purple Bishop.
To replicate the ratio trigger: divide the current standard deviation by its value from 5 bars ago. When that ratio crosses 2, the Purple Bishop has fired. In Pine Script this is a single line. In TradingView you can plot it as a separate indicator and set an alert on the threshold.
The Purple Bishop does not tell you where to enter. It tells you the market has changed character — the bars are no longer moving with the same force they were 5 bars ago. What you do with that information depends on where the Queen is and what the other pieces are showing. Read the full board.