**This is an old revision of the document!**

This is a simple tool for plotting a straight line graph.Your plot will always appear on a new tab. This makes it easy to come back to this page, change something and resubmit for a new graph.

## How it works

A php script takes the inputs you enter and formats it into instructions which are fed to Gnuplot to produce your plot. Gnuplot is a **free** and powerful plotting program and can do quite a lot more than we're using it for here. You might like to check it out if you're interested in this kind of thing. Other plotting programs commonly used by physicists include Microcal Origin (powerful but expensive) or Microsoft Excel (not the best, but on just about every computer in the world).

## What's the fit doing?

When the computer makes a fit it is using a technique called linear regression using a least squares approach. The computer tries to find the line where the sum of the squares of the differences between the line and the data points is the smallest and calls this the line of best fit.