Enter your data points in the columns labelled "x" and "y". You can enter up to 10 points. Enter zeroes for any points you don't need. Then put the number of data points you entered in cell B14 (next to the label "n"). Everything else should be recalculated automatically. The data points and best fit line will show up on the graph. If you make a mistake, the calculator might stop working. In that case, just reload this page and start again. You can adjust the zoom level of the graph by right-clicking (or command-clicking).