Convert MAP sensor output voltage to a usable manifold absolute pressure (MAP) value using linear modeling and calibration data.

## Linear Model

MAP sensors produce a linear voltage output across the operating range. The standard form uses the equation:

**y = mx + b**

Where:
- **y** = Output voltage (V)
- **x** = Pressure value (in Hg)
- **m** = Slope (typically −0.1 V per in Hg)
- **b** = Y-intercept (reference voltage)

### Helm Manual Specification

Based on factory documentation:

**y = (−0.1)x + 2.85V**

Solving for pressure:

**(−0.1)x = y − 2.85**

**x = (y − 2.85V) / (−0.1)**

## Calibration Data Comparison

The following table compares three calibration sources: OEM specifications, Helm manual formula, and measured sensor data.

| Pressure | Alldata Spec | Helm Formula | Measured Value |
|----------|--------------|--------------|----------------|
| 5 in Hg  | 2.5V         | 2.35V        | 2.460V         |
| 10 in Hg | 2.0V         | 1.85V        | 1.938V         |
| 15 in Hg | 1.5V         | 1.35V        | 1.509V         |
| 20 in Hg | 1.0V         | 0.85V        | 1.012V         |
| 25 in Hg | 0.5V         | 0.35V        | 0.558V         |

## Alldata Specification

OEM data sources publish the following formula:

**x = (y − 3.0V) / (−0.1)**

> [!IMPORTANT]
> The Helm manual and Alldata specifications differ slightly. Use the formula that best matches your calibration data. The Helm equation typically provides good results for stock sensors, while Alldata may better represent specific OEM sensor batches.

## Calibration Approach

When calibrating your sensor:

1. Measure voltage output across the full operating range (idle to WOT vacuum)
2. Compare measured values to both formulas
3. Select the equation that provides the closest correlation
4. Verify calibration by cross-referencing with known pressure values

> [!TIP]
> If measured values fall between the two formulas, consider establishing a custom calibration curve based on your actual sensor data for maximum accuracy.