Curriculum·R403 Risk Management as the Actual Product·about 33 min
Circuit breakers
By the end of this lesson you can
- →Define a circuit breaker as a rule that acts without requiring a judgment
- →Compute what a loss limit would have cost against what its absence did
- →Derive a daily limit from your win rate and trade frequency rather than picking one
- →Distinguish an alert, which needs a human, from a breaker, which does not
Senior · enrolled learners
This lesson opens with Knight Capital, 1 August 2012.
- What happened
- During a deployment beginning 27 July 2012, a Knight Capital technician did not copy new routing code to one of the eight servers running its order routing system. That server retained dormant code from 2003 whose safety checks had been disabled by a change in 2005. When the market opened on 1 August the untouched server began sending orders continuously, executing roughly 4 million trades in 154 stocks totaling more than 397 million shares, buying high and selling low at a rate near $10M a minute. An internal system had sent 97 automated emails referencing the router before the open, identifying an error, and no one acted on them. The firm had no kill switch, no automated circuit breaker and no pre-set capital threshold that would halt trading after a given loss. About $440M was lost in 45 minutes. The SEC charged Knight with violations of the market access rule and it settled for $12M. The firm required emergency funding and lost its independence.
- The decision point
- Every input needed to stop this existed inside the firm. The error was detectable before the market opened, the losses were visible in real time, and the position was reversible for the first several minutes. What did not exist was a rule that acted without a person deciding to act. A control that requires somebody to notice, understand and choose is not a circuit breaker, it is an alert, and the firm had 97 of those.
- Recorded loss
- $440,000,000
What you will be able to answer
- →What is a circuit breaker?
- →What would a limit have cost Knight?
- →How do you set a daily limit?
- →Alert or breaker?
Orientation and Year One are open: anyone can read them without an account. From Year Two onward the lessons are for enrolled learners, because progress through the later years only means anything if it is tracked against a record.
It is free. We do not sell the list and there is nothing to buy at the end of it.
Sources and review
- https://www.sec.gov/newsroom/press-releases/2013-222
- https://www.sec.gov/files/litigation/admin/2013/34-70694.pdf
- https://www.henricodolfing.ch/en/case-study-4-the-440-million-software-error-at-knight-capital/
- https://dougseven.com/2014/04/17/knightmare-a-devops-cautionary-tale/
Confidence high·Volatility low·Reviewed 2026-08-07·Owner unassigned
Contested
The Knight loss is reported as $440M and as $460M depending on whether the figure is the trading loss or the total including related costs. The SEC order and most accounts use $440M and that figure is used here.
The trigger-frequency arithmetic in part three assumes independent trades at a constant win rate. Real outcomes cluster, which makes a given limit trigger more often than the binomial figure. That makes the derived limits conservative in the wrong direction, so per R403-L the correct version is simulated on your own record.
S207-06 owns policy decisions made in advance at Sophomore level. R411-05 implements these controls inside an automated system. This lesson owns the design of the thresholds. Keep the split.