# Measurement System Documentation

This system provides a flexible way to store, retrieve, and analyze measurement data using a chainable API.

## Basic Usage

```javascript
const { MeasurementContainer } = require('./index');
const container = new MeasurementContainer({ windowSize: 20 });

// Set values
container.type('pressure').variant('measured').position('upstream').value(100).unit('psi');

// Get values
const upstreamPressure = container.type('pressure').variant('measured').position('upstream').getCurrentValue();
console.log(`Upstream pressure: ${upstreamPressure}`);
```

## Chainable API Methods

### Setting Context
- `type(typeName)` - Set the measurement type (pressure, flow, etc.)
- `variant(variantName)` - Set the variant (measured, predicted, etc.)
- `position(positionName)` - Set the position (upstream, downstream, etc.)

### Setting Data
- `value(val, [timestamp])` - Add a value with optional timestamp
- `unit(unitName)` - Set the measurement unit

### Getting Data
- `get()` - Get the measurement object
- `getCurrentValue()` - Get the most recent value
- `getAverage()` - Calculate average of all values
- `getMin()` - Get minimum value
- `getMax()` - Get maximum value

### Calculations
- `difference()` - Calculate difference between upstream and downstream positions

### Listing Available Data
- `getTypes()` - Get all measurement types 
- `listVariants()` - List variants for current type
- `listPositions()` - List positions for current type and variant

## Example Workflows

### Setting and retrieving values
```javascript
// Set a measurement
container.type('flow')
         .variant('measured')
         .position('upstream')
         .value(120)
         .unit('gpm');

// Retrieve the same measurement
const flow = container.type('flow')
                     .variant('measured')
                     .position('upstream')
                     .getCurrentValue();
```

### Calculating differences
```javascript
// Set upstream and downstream measurements
container.type('pressure').variant('measured').position('upstream').value(100).unit('psi');
container.type('pressure').variant('measured').position('downstream').value(95).unit('psi');

// Calculate the difference
const diff = container.type('pressure').variant('measured').difference();
console.log(`Pressure drop: ${diff.currentDiff} ${diff.unit}`);
```

### Working with historical data
```javascript
// Add multiple values
container.type('temperature')
         .variant('measured')
         .position('outlet')
         .value(72)
         .value(74)
         .value(73)
         .unit('F');

// Get statistics
const avg = container.type('temperature').variant('measured').position('outlet').getAverage();
const min = container.type('temperature').variant('measured').position('outlet').getMin();
const max = container.type('temperature').variant('measured').position('outlet').getMax();
```