# XWUIChartThresholdReferenceLine

A threshold reference-line chart: a fixed-type wrapper around `XWUIChart` that plots series and overlays a horizontal reference or threshold line, making it obvious which points sit above or below a target. Supply `{ series }` of `{ x, y }` points plus a `block` preset (1-4) and `size`. Use it for targets, limits, or SLAs where crossing a fixed level is what matters.

## Basic Usage

This example plots the two series, Series A and Series B, across their six monthly points (Jan through Jun) and lays a horizontal reference line across them, so the months that rise above or fall below the threshold stand out at medium size.

```example
file: examples/BasicUsage.ts
html: examples/BasicUsage.html
title: Basic Usage
description: The two series plotted with a reference line across the two monthly series, marking which Jan-Jun points clear the threshold.
```

## API Latency vs SLA

Plots hourly p95 API latency against a dashed 80ms SLA line with a shaded breach zone above it, so the midday hours that cross the limit are immediately obvious.

```example
file: examples/ApiLatencySla.ts
html: examples/ApiLatencySla.html
title: API Latency vs SLA
description: Hourly p95 latency with a dashed SLA lineY annotation and a red breach-zone region.
```

## Blood Pressure vs Healthy Band

Tracks a week of systolic and diastolic readings against a shaded healthy band and a red hypertension threshold line, flagging the midweek days that climb out of range.

```example
file: examples/BloodPressure.ts
html: examples/BloodPressure.html
title: Blood Pressure vs Healthy Band
description: Systolic and diastolic series with a healthy-range region annotation and a hypertension lineY threshold.
```

```api
```