# How to use Curve Fit Online Tool?

This is an online tool for curve fitting.

Usage:

1. Type X and Y values. You can add rows to the table by using the button below the table.

2. Choose fit method using the dropdown menu.

3. Results are generated automatically.

You can:

- export the report to PDF using "GENERATE PDF" button.

- export the report to TXT using "EXPORT TXT" button.

- manipulate diagram (for example zoom in or out)

- save diagram as PNG.

Contact: [email protected]

## Four Parameter Logistic (4PL) Curve Calculator Documentation

### Four Parameters Logistic Curve

Four parameters logistic model (4PL) is often used in modelling of many biological systems. As the result of fitting, an S-shaped curve is obtained. The formula used for fitting is the following:

$y = \frac{a - d}{1 + (\frac{x}{c})^b} + d$

where:

**a** - the minimum value that can be obtained (y at x = 0)

**b** - Hill’s slope of the curve

**c** - the point of inflection (i.e., the point on the curve halfway between a and d)

**d** - the maximum value that can be obtained (y at x tending to infinity)

### Data Input

Type the data into the table on the left side of the application. The first column is for **x**, which is an independent variable, and the second column is for **y**, which is a dependent variable. You can add rows if you want to introduce more data. You can also paste a dataset from an Excel worksheet using the shortcuts **LCTRL+C** (Copy) and **LCTRL+V** (Paste).

### Calculation

The best-fit line is calculated automatically. The results are shown below the data table.

### Visualize a graph

The fitted curve is visualized automatically. You can export the chart to a png file. Set the graph title and axis labels according to your needs.

A tutorial how to use the Curve Fitting Tool: https://youtu.be/dd2gJ-KSkTU