Fit and display ranges#

Trendlines have two independent X ranges. Keeping them separate lets you decide which observations determine the model and where the resulting curve should be visible.

Fit range#

Fit range selects the source-dataset points used to calculate coefficients. Its From X and To X endpoints are inclusive: a point at either endpoint is included. GraphX applies this selection before model-specific domain validation, so only selected points need to meet a logarithmic, exponential, or power model’s requirements.

For a newly created trend, the default fit range is the calibrated X extent. This makes the configured fitting domain clear even if the dataset itself occupies only part of the calibrated graph. Changing a fit range changes the selected points, coefficients, R², fitted-point count, and fitted-data X range.

The range must contain finite numbers with From X less than To X. A fit needs at least two selected finite graph-coordinate points; polynomial order $n$ needs at least $n+1$.

Display range#

Display range chooses where GraphX draws samples of the already-fitted function. It does not select data points and does not change coefficients, R², or the number of points fitted.

By default, GraphX displays from the smallest to the largest finite X coordinate in the source dataset. This normally avoids drawing an extrapolated segment immediately, while allowing the calibrated fit domain to be wider than the observations. The display range must be finite with From X less than To X. Logarithmic and power models additionally require a positive display X range.

Example#

Suppose the calibrated X limits are 0–100, but reliable observations are only from 20–80. You might:

1. Set Fit range to 20–80 to calculate the model from those points only.
2. Set Display range to 20–80 to show only the supported interval.
3. Optionally extend Display range to 10–90 to inspect the model outside that interval.

Step 3 does not refit the model. It only draws more of the same function.

Extrapolation indication#

GraphX shows Includes extrapolation when the configured display range extends beyond the configured fit range. It compares the two configured domains, not merely the outermost X values of the points that happened to be selected.

For example, a fit range of 0–100 and display range of 10–90 is not marked as extrapolation even if the nearest actual data points are at 20 and 80. A display range of -10–100 or 0–110 is marked, because it extends beyond the fitting domain.

An extrapolation indication is a reminder to assess the model carefully. It is not an error and does not stop GraphX from drawing or exporting the trendline.

Editing ranges#

While you type a range endpoint, GraphX keeps an incomplete or invalid draft visible so you can finish the number. It applies a change only when the pair of endpoints forms a valid range; leaving an incomplete entry restores the last valid value. This prevents a temporary partial edit from silently changing a fit.