When you need to use it in the lab this plotting tool may already be built into the online lab manual, possibly with some modifications. In case it is not there, or if you need/want to try it out with some other data, we've put it here. Your plot will always appear on a new tab.

## How it works

A php script takes the inputs you enter and formats them into instructions that are fed to Gnuplot to produce your plot. Gnuplot is a **free** and powerful plotting program and can do quite a lot more than what 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 it's likely on most computers you'll be using. If it's not you can download a freeware “workalike” version of the Microsoft Office package that's called *OpenOffice*. Its Excel-like spreadsheet is called Calc.)

## 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.