# Drawdown — Peak-to-Trough Decline Tracking
**Tracks peak value and current/maximum drawdown.** Core risk metric
for circuit breakers.
| Update cost | ~5 cycles |
| Memory | ~24 bytes |
| Types | `DrawdownF64`, `DrawdownI64` |
| Output | Current drawdown value |
| Error handling | Returns `Result<_, DataError>` on NaN/Inf input |
## What It Does
```
Value
100 ┤──────────┐
90 ┤ │ peak = 100
80 ┤ │╲
70 ┤ │ ╲────╱╲
60 ┤ │ ╲──── drawdown = 40 (peak - current)
│ │
│ max_drawdown = 40 (worst ever observed)
└──────────────────────────────────────── t
```
Tracks three values: peak (highest value seen), current drawdown
(peak - last sample), and maximum drawdown (worst drawdown ever).
## When to Use It
- Risk circuit breaker: "halt if PnL drops $X from peak"
- High-water mark tracking for fee calculation
- Maximum adverse excursion analysis
## Configuration
```rust
let mut dd = DrawdownF64::new();
dd.update(100.0).unwrap(); // peak = 100, drawdown = 0
dd.update(90.0).unwrap(); // peak = 100, drawdown = 10
dd.update(95.0).unwrap(); // peak = 100, drawdown = 5
dd.update(60.0).unwrap(); // peak = 100, drawdown = 40
assert_eq!(dd.max_drawdown(), 40.0);
dd.update(110.0).unwrap(); // NEW peak = 110, drawdown = 0
```
Zero config — just create and update. Implements `Default`.
## Performance
| `DrawdownF64::update` | 5 cycles | 5 cycles |
One comparison + one conditional update. Pure arithmetic.