# Subtract by IoSource data

## Summary
Subtract a DataBundle element by a subtrahend loaded from a data source

## Metadata
- **Module ID:** SubtractBySourceData
- **Module path:** /home/runner/work/MoDaCor/MoDaCor/src/modacor/modules/base_modules/subtract.py
- **Module version:** 20251029.1
- **Keywords:** subtract, scalar, array

## Required data keys
- signal

## Modifies
- **signal**: signal, uncertainties, units

## Required arguments
- _None_

## Default configuration
```json
{
  "subtrahend_source": null,
  "subtrahend_uncertainties_sources": {},
  "subtrahend_units_source": null
}
```

## Argument specification
| Argument | Type | Required | Default | Description |
|---|---|---|---|---|
| `subtrahend_source` | str | No | - | IoSources key for the subtrahend signal. |
| `subtrahend_uncertainties_sources` | dict | No | {} | Mapping of uncertainty name to IoSources key. |
| `subtrahend_units_source` | str | No | - | IoSources key for subtrahend units metadata. |

## References
DOI 10.1088/0953-8984/25/38/383201

## Notes
This loads a scalar (value, units and uncertainty)
            from an IOSource and applies it to the data signal