# 📉 regressionSlope()

Calculates the slope of the best-fit line through a numeric column.

## 🔹 Signature

~~~js
column.regressionSlope(customX = null)
~~~

## 🔹 Description
Returns the slope of the regression line between:
- `this` column (Y)
- `customX` or the default `xValues = [1, 2, ..., n]`

## 🔹 Example

~~~js
const col = Statistics.newColumn([2, 4, 6]);
console.log(col.regressionSlope()); // 2
~~~

If `customX` is not provided, `[1, 2, 3]` is used.